Sunday, October 6, 2019


Not necessarily realized potential, but potential.  I don't want to take yet another set of boring pics of my van simply parked in front of street art, duh.  I'm trying to create moments that actually make sense, with the van in the art.  But you have to remember that making a 10-foot-tall, 23-foot-long whale of a vehicle appear like it actually belongs in any given scene is not an easy thing.  Especially when one is surrounded by homeless handout petitioners, relentless street hustlers, other gaping groups of touristy people waiting for their turn to snap a pic, and various and sundry other distractions and impediments.

Here are a few shots from my first such attempt in Houston's Old Chinatown this morning.

It's parked right under the concrete awning, like the awning was made to fit the roof.
This was one of the original Houston murals that started the craze.  It's a bit faded by now, and doesn't lend itself to easy composition. 
The shape and color of this building with the inset black echoes the inset black of the van windows, but I haven't figured out how to frame it yet.
One of my favorite reflection shots. 
Another reflection, off the rear windows this time.
Not much artistry in this one, but OMG - an astronaut cuddling an armadillo with an oil derrick reflected in his visor - who could resist such Houstoniana?!
Interstate as pillow for that medusa head, perhaps?
Anyway, more for me to noodle on, the next time I feel like taking an early Sunday morning jaunt downtown.

Tuesday, May 14, 2019


The story I tell below, I already knew it.  And I knew that everyone who has experience with T1N Sprinter towing knows it, if they happen to be upfitted.  But here it is in detail for the record, so that it will hopefully save someone else some pain, anguish and expense:
  1. T1N upfits can never, ever, EVER be dragged.  They have to be flat-bedded.  Whatever they have in their rear ends cannot be subjected to a near-ground experience, be it a generator, water tanks, whatever.  If it's a T1N upfit, by definition it's packed with stuff under there.  Just forget the whole idea of dragging it.  
  2. Every time you call a tow, even if you are successful in getting a flat-bed on first request, you are probably going to get one which is almost unworkably small.  The one shown in the pics below can take up to a 22 foot vehicle and 10,000 pounds, and that's typically what they send in scenarios like the one I had today.  BUT - and this is the important part - inexperienced tow operators often don't know that they need really, really big shims to accomplish a successful tow of a 22' upfit T1N Sprinter.
It's that simple.  Shims, or you're screwed  - take your pick.  

By shims, I mean lengths of really heavy lumber, preferably hardwood because we are talking about one ton per tire, which can shallow up the tow bed angle enough to get this kind of job successfully done.

Let me walk you step by step through my mishap so that you can understand exactly what I mean.

So this afternoon, I'm heading east on TX-71 between Bastrop and Smithville when all of a sudden, my engine blows up, basically.  By the grace of God, I manage to get safely off the highway.
How many times have I seen this particular view?  Ugh.
If your T1N unexpectedly blows up for no apparent reason despite the thousands of dollars of bulletproofing you've done on it, the best thing you could do is get your lead mechanic on the phone ASAP.  For me, that is Joel Sell, aka Million Mile Sprinter.

I emailed Joel a 6-second video of the engine plus a description.  Clearly it lost turbo, but it didn't feel to me like a normal turbo issue.  The van was running rough like I've never seen it do, and I had even less functionality at my disposal than I would during a regular limp home mode (LHM).  I've driven a hundred miles in LHM.  It's ugly, but it can be done.  This thing I was confronted with today... I was never going to make it down the road. 

OK, so, Joel's recommendation was to flat bed it the hell out of there.  I concurred.  I got with my roadside assistance (I use Good Sam) and arranged for a tow.  

It actually showed up as a flat-bed, but not the larger size I was hoping for.  Technically, this size can haul a T1N Sprinter as I said.  It's just a poor idea to try.

You can immediately sense a departure angle issue. 

Incidentally, I'm not revealing the tow operator, because I feel bad for the guy.  He was a really nice guy and he tried his best, but he was young and inexperienced, and he didn't have the right materials in his kit.  I'll tell you what - he will be a lot more experienced when he wakes up tomorrow vs. waking up this morning.

OK, so, both the terrain and the substrate were favorable for the load-out despite the departure angle problem.  The van's skid plates dug in, but this part of it was do-able without too much drama, as you can see here.
Uh-huh.  You see the problem.  That angle is just way too unforgiving. 
In this next pic, you see what a T1N looks like on the back of this kind of flatbed.  It's really too big even if it's legal.
There's just too much hanging off the back of that tow truck.
Because I was remaining overnight with my van, Freightliner would not allow me within their fenceline.  Therefore, the tow operator had to deposit this load on the public street in front of Freightliner.  That's where things got ugly, because the off-loading environment was not as forgiving as the on-loading environment had been.
I say again:  I haven't spent the last 4.5 years on internet forums for nothing.  WE KNOW from experience that we need shims for this.  I went into the Freightliner business, and scrounged up what wood scraps I could find.

There's a little piece of wood, but that's not going to get this job done. 

Not this either, although that was a nice piece of hardwood dunnage.

Next!  Nope; not this either.

Here's a close-up showing the skid plates and how they were carving out their own little trenches in the asphalt.  On an ordinary day, I would have gotten down on the ground with my wrench and removed those skid plates.  But once the thing is in tow under someone else's control, for liability reasons, I can't touch it.  So we were stuck with this status quo.  

Then things went from bad to worse, as this picture suggests.  Do you see how there is a GAP between the bottom of the flatbed and the top of the pavement?  That's because, without proper shims, the operator had no choice but to basically roll the tow truck out from under the T1N Sprinter.  This is highly dangerous, but given the materials at hand, it was difficult to identify an alternative in the moment

It was not going that badly, until he lost control of it.  Remember, the Sprinter has to have its transmission in neutral during this process.  And it's on this angle.  So, without his ability to keep tension on the tow line, that Sprinter is going for a ride under the power of nobody.  Which is exactly what it did.  It dropped off the flat bed, rolled backwards, and plowed arse-first into a Freightliner that happened to be parked at the curb behind us.  It literally bounced off the Freightliner and landed in the position you see here.

I have to have my husband evaluate this further, but at first glance, the score was Sprinter 1, Freightliner 0.  The Freightliner's bumper wasn't nearly as robust as the custom hitch carrier that my husband had welded up to be as strong as a proverbial brick shit house (excuse my language, but there's no other way to put it).  The bumper cover ended up askew.  Do you see how it's gapping at the far left, more so than on the right side under the headlight?   Uh-huh. 

Anyway, frankly I'm glad the Freightliner was there to serve as our collision post, because I'm not sure where my Sprinter would have stopped rolling otherwise.  

My front end (ground effects) was also damaged by the tow cable during this run-away event.  It's nothing that can't be fixed, but it's a pain. 
Fiberglass mess.


When roadside assistance is paying the bill, the tow companies are going to want to send the smallest flatbed they can to do this job, and it's a penny-wise pound-foolish decision.  Whatever they save in equipment costs, they are highly likely to incur ten-fold in damages.  Unless they carry really long heavy wooden shims, stuff like this is always going to happen.  

Of course I knew that years before today, and obviously after today I'm going to consider transporting MY OWN shims, possibly under the chassis.  Because my van, you see, keeps breaking down.  No matter how hard I try, nor how much money I spend on it, it just keeps happening.  So far, at least.  Maybe when I finally get to Million Mile Sprinter later this summer, I can finally make some bulletproofing headway.

Oh, and by the way, I don't know what's wrong with it yet.  I'm camped out in front of a Freightliner that is unknown to me, in a city that is not mine, waiting until they open in the morning so that they can look at it. 

Friday, February 8, 2019


OK, I’m going to describe the facts of our fraud experience as succinctly as I can, in a timeline format (all dates 2019).

TL;DR – Incredibly strong circumstantial evidence suggests that my husband got frauded during the purchase of an AT&T Mobley device which is currently being offered at a promotional price.  AT&T has voided over $2,000 in scam charges to his account, but we don’t know how much of my husband’s personal information has been compromised in this process.  I advise Mobley owners to watch their own AT&T accounts carefully for evidence of this type of fraud.  It’s not the Mobley device itself that is the locus of this scam – the scammers are apparently adding unauthorized additional lines to AT&T accounts at the same time as they are adding the legitimate Mobley lines.  And then they rack up extreme charges on those additional lines very quickly, knowing that they are going to be detected and shut down soon enough.  We have no idea how widespread this fraud is.

DETAILS (all dates are 2019)

(1) On Thursday January 31, my husband went through the contractual process of ordering a Mobley for inclusion on his AT&T cellular account.  This is a popular cellular internet device used by vehicle owners.  You can read about the deal on this Sprinter Forum post, for example (and there are many others).

(2) Our Mobley device was shipped on Tuesday February 5.

(3) The Mobley was delivered to our home in Texas on Wednesday February 6.  The phone number associated with our Mobley is 409-204-9xxx (x’s for our privacy).

(4) Due to our work schedules, we could not activate our new Mobley right away.  We set it aside to deal with it on the coming weekend.

(5) On the morning of Friday February 8 (i.e., today), my husband received two text messages from AT&T (from the real AT&T - not from a scammer) telling him that he owed in excess of $1,000 in international roaming charges on each of two cellular lines on his account.  The numbers of those two lines were 409-204-9284 and 409-204-9285.  Note that they are almost sequential to the number that was legitimately issued in conjunction with our Mobley.

(6) Upon contacting AT&T, my husband was told that “someone” working “online” had fraudulently added these additional two lines to his account on February 4, the day before our Mobley shipped (and I bet this unauthorized addition occurred at the exact same time that our Mobley hardware device was configured).  AT&T voided those other two lines with the excessive charges, placing the SIM numbers on a global blacklist.

(7) AT&T revealed no further details about this fraud.

In my opinion, the circumstantial evidence supports the conclusion that the Mobley sellers frauded my husband - that circumstantial evidence is *overwhelming*.  The timeline is to the day, and the cell numbers are almost exactly sequential!!!  Duh!!

(8) My husband now has to monitor his credit rating etc. to ensure that no further breaches occur going forward.  It’s not clear how much of his personal data the Mobley sellers have accessed at this point.  Clearly, they got hold of enough information to transact thousands of dollars of scam in his name before they were shut down.

Good luck to you fellow Mobley owners.

Too late for us, hopefully not for you. 
I love this meme below - good question!

EDIT 20190211 - AT&T told my husband on Feb 8, 2019 that the fraud was resolved.  But when he logged in and re-checked on Feb 10, the charges were still there.  Worse, they would have autodrafted in another 3 days if he hadn't stopped that from happening.

No more autodraft!!  It's too dangerous, obviously!  If the autodraft of these frauded charges had gone through, our mortgage payment might have bounded, and then it would have been goodbye credit score.
AT&T forum thread on this topic:

EDIT:  I'm just going to leave this update here.  This says it all.

Sunday, January 27, 2019


Every good project starts with an inspiration photo.  This cluttered and inefficient image from last summer was mine:
Dog be like, "Whut??"
That photo shows the laundry drying under the awning by being stuck to the side of the van with individual magnets.  And it shows a wilderness-built cooking table (which should be kept next to the fire pit) being used to hold what our little folding aluminum camp table is too small to accommodate.

You might wonder why, in an infinite sea of trees, I'd choose to stick laundry to the side of the van for drying.  Well, in that part of the world, rain showers come frequently and without warning.  It is simply more effective to stick it under the awning where I do not have to worry about it getting soaked unexpectedly.  

I decided I would build a sideboard to serve both of the identified needs - to provide more storage for pots, pans, drinks, condiments, etc. during meals, and to double as a drying rack for laundry.

There was no doubt in my mind about what material would comprise the sideboard - I used the same perforated aluminum out of which I'd constructed our under-cabinet suspended shelves, our Lagun table, and the ventilation cover on our lithium battery chamber.
Consistency is NOT the hobgoblin of little minds, thank you. 
Here's a photo tour of this project, including sourcing. 
That's the spec on the one-eighth aluminum, which I got in a 1' x 2' sheet from Online Metals
Given that this device was intended to hang on the exterior side of the van, there were a couple of unusual operational considerations.  

First, the sideboard had to be strong enough to support at least 10 pounds of stuff without either falling off or skidding down the side of the van under the weight.  To support the main mass, I used the same "skyhook" magnets as I had found to be effective for the awning screen surround that I designed a few years ago.  These are rubber-backed and, as long as you observe good neodym hygiene, your scratches should be minimal.  

By "hygiene" I mean, do NOT leave these things lying around.  They will pick up every speck of magnetize-able dust and every iron shaving that they can find within about a one-mile radius.  It's not really the magnet itself that has the potential to scratch your paint - it's what gets trapped between the magnet and the van.  They have to be kept very clean, which is a challenge given the power they exert on their surroundings.    
The pictured object is a Master Magnetics 7580 Magnetic Hook Organizer, which has a 65 pound pull force. The quote is from someone's hacked Wonka transcription
The hooks look like this in application - just a simple knotted loop to keep the suspension lines in place.
That's a brother from another mother in the reflection above the hook - an Amazon delivery Sprinter with its headlights on. 
Second, obviously I could not have a bare cut aluminum table edge bumping up against the side of the van - that would be a disaster for the paint.  The body contact had to be with a soft non-abrasive surface.  My husband and I first used a jigsaw to round the corners of this sheet (for visual consistency with the Lagun table) and then I edged in in Dritz 1" charcoal gray polyester belt webbing, which is the same treatment I had given to the Lagun top (belt webbing has about a million uses in a van).

Third, for similar scratch-prevention reasons, I could not allow any suspension hardware to touch the van, so it had to be inset.  The beauty of perforated aluminum is that it provides an infinite number of possible configurations without the need for drilling holes.
There's a close-up of the belt webbing which I bound into place with embroidery floss, and a Strapworks stainless steel D-ring with clip bolted behind it. 
I used one of those D-rings inset into each rounded corner.  In order to make for easy assembly, disassembly, and storage, I decided that the suspension lines needed to be detachable, so I used Strapworks' half-inch miniature bolt snaps at the four corners.  The tiny bolt snaps will remain connected to the lines at all times, whether in use or in storage. 

My suspension lines are made of orange paracord.  In the realm of artistic design, ordinarily one might not choose to combine orange with the garnet color of our rig's side stripe - those two don't necessarily go together.  But the orange design element was already present in the form of reflectors and the signal glasses on the van.  If you can't beat 'em, join 'em - I ran with safety orange in getting an CG Gear sand-free mat (I cut an 8' x 8' into two halves and re-edged the cut seams, also with belt webbing) and in using the paracord.  I also like the photo ops that this combo provides in cross-referencing camp fires.
Best orange ever.  Orange accessories would have made for a nice photo with this, if I'd had them at the time it was taken. 
Getting those lines the correct length took a long time and many careful iterations.  The van body is curved, plus in my driveway it was parked on a slope, so it was basically impossible to get it level in situ.
Nice try, but too many variables to be useful. 
I achieved level by hanging it on the side of my upright freezer and working on it there, given that the freezer was more conveniently plumb and level.

In order to keep the table from slipping fore and aft when it hangs on the side of the van, I used orthogonally-magnetized neodyms as "keepers" on the edge of the sideboard that fit into the van's lateral body groove.  By this I mean, the north and south poles of the magnets were oriented out the sides, not out the top and bottom face as they typically are.
See the little red and green cartoon at the upper right corner?  That's what I mean.
Image from KJ Magnetics.  
I needed two of those 2-hole countersunk block magnets to stabilize the edge that was up against the van body.  For better and for worse, each of those blocks has a 17-pound pull force (smaller ones were not available with sideways magnetization).  Trust me when I say that this table is not going anywhere.  I could probably drive at freeway speed with it in place, having 2 x 64-pound suspension hooks and 2 x 17-pound lateral stabilizing magnets on it!  

Here's what one of those countersunk blocks looks like in place.  Note that the edge of the table snugs into the Sprinter's body groove, as I mentioned above.  That allows the side-mounted neodym block to get close enough to grab the metal, but the majority of the force is exerted by the web-woven table edge, to minimize scratches.

Fun blog post for me, as these materials are so photogenic.
Here are a couple of money shots of the table in place.  

Dinner is not yet served, but it will be.  

Yeah, I can support all that weight, baby. Bring it!!
The sideboard is easy to reach from those "butt bucket" REI camp chairs (aka Flexlite chairs) that we typically carry lashed underneath our under-cabinet suspended shelves:
Yup, I can reach it easily.
When it's time to dry laundry, I simply raise this sideboard up and suspend it from the top of the van body.
Much better looking than having individual pieces of clothing strewn all over the side of the van.  More effective for drying, too. 
It was windy when that photo was taken; you can see the clothes being blown forward a bit.  I'm using well-rated folding travel hangers for this hanging purpose.  The points do not insert into the perforated aluminum holes, but they do catch in the edge of the holes, so in light winds, they won't blow off.

How often do you see 5 stars anywhere on Amazon?!
The sideboard's drying utility is not just limited to hanging.  Because the perforated aluminum is 40% open space, socks, gloves, etc. small items can be dried on top of it while the other items hang underneath.

When I raise the sideboard up high as shown above, the countersunk neodym side magnets will no longer touch the van's steel side body because the windows sit proud of the van.  I solved that issue by using a KJ Magnetics plastic-coated disc as follows, in order to keep the sideboard from swaying in the wind (the clothing could act as sails) and potentially scratching the windows:
The neodym black disc attracts to one of the two lateral magnets, which is enough to stop it from moving around. 
We used Slide-co spring-loaded mirror clips to mount this table for storage.  At long last, I have something to break up the monolithic appearance of the butt end of this galley cabinet.  I've always found that orange atrocity to be a visual distraction.  With its Lagun table big sister hanging nearby (the Lagun top stores on our wet bath door), the sideboard looks like it was intended to be in this space all along.  The space finally appears visually coherent and complete.

Close up:
Almost no other object could be stored in this space due to the sliding door clearance issue.  But this sideboard fits perfectly.
You'll notice that I detached the suspension lines and hung them a few inches right of this sideboard for storage.  The two neodym suspension hook magnets are right above them. 

Next will come the off-grid road testing of this new asset, but our big trip won't be for a few more months.  All of my current projects are in preparation for returning to this little piece of paradise:

Thursday, January 24, 2019


Following on Part 1 which described the general configuration of our DIY electrical system, and Part 2 which dealt with the AC system, here's the diagram for the charging and inverter portions of our system.  Relevant forum cross-references:  My husband's original electrical system development Air Forums thread here, and a Sprinter Forum lithium thread here.

As with my first two posts, I'll recap the general operation by describing the components individually.  The superscripted component numbers on this diagram correspond to the numbered paragraphs below it.
Click or tap image to expand size for clarity.  Blogger downsamples embedded images. 
13.  Engine alternator - For as long as we retained the original OEM single-AGM Lifeline house battery in our rig, we had no need to change or upgrade the alternator.  Shortly after converting to lithium iron phosphate (LiFePO4) battery (described below), we installed a Bosch 200 A alternator which, when used with a battery-to-battery charger (also described below), theoretically should be able to integrate seamlessly and charge the lithium battery when the van's engine is running.  However, as is often the case in cutting-edge conversions, there have been complexities, most notably the premature failure of the alternator's clutch pulley, which I describe in this post.  I will have more to say about alternator management in the future.

14.  Chassis battery - Nothing fancy here, just an ordinary EverStart truck battery from Walmart.  Chassis batteries don't last in the deep south, and with their climate-limited lifespans, I've never seen fit to buy anything more expensive.
Welcome to the red zone.  Diagram courtesy of Tiresplus and yes, I've always found it to be accurate.  Not changing a battery at 30 months here is to risk being stranded.  I often do it at 24 months. 
15.  Battery relay - The purpose of this device is to isolate the house system from the chassis system when the engine is not running.  This is a Mercedes Benz (MB) component that was already present in the vehicle as OEM equipment.  It had been used by Airstream to isolate the original lead-acid single house battery.  These types of relays are sometimes called battery isolation modules (BIMs).

16.  Battery-to-battery charger - This Sterling limits the load to 60 A and bumps the voltage up to 14.6, which is what the lithium battery prefers to charge at.  There is sometimes uncertainty about which of Sterling's products we've used (they don't seem to number their products very clearly), so here is a close-up photo:

17.  Lithium charger - This Progressive Dynamics Inteli-Power PD9100L Series unit accepts 120V AC and converts it to 14.6V DC with a maximum input current of 60A (again, 14.6V DC is the voltage at which the lithium battery charges most efficiently).  We installed this to retain the option of charging the lithium battery from a shore power source.  As we have learned again and again, it is essential that off-grid vans incorporate as much systemic redundancy as possible.  Something will fail - it's just a matter of what and when - so you better have a Plan B.  In our case, we also have Plans C and D, because our system allows 4-way charging - solar, alternator, generator, and shore. When we originally installed this charger, we never actually intended to connect to shore power - it was just there for emergencies.  But, heh heh, we've done it, especially following the alternator clutch pulley failure described above.

18.  Solar Panels - Our Grape Solar GS-S-100-TS 100 watt monocrystalline panels are wonderful, and I'm very glad we managed to get them before supplies were exhausted.  They are no longer manufactured in the size (aspect ratio) that was ideal for installation on our roof.
They straddled our OEM stainless steel roof rack like they were made for it.
These monocrystalline panels were also noteworthy in the high efficiency that they offered (18.3%).  Knowing that they would be discontinued, we bought two extras and put them in storage for potential future use.

19.  Switches - The Blue Sea manual battery switches were inserted so that we would have the option to disable charging on PV1 or PV2 circuits on the BMS described below.  We like Blue Sea products, which are ruggedly made for marine applications and are good quality.

20.  Battery Management System (BMS) - This is an Electrodacus SBMS-100, currently out of production but its builder still offers comparable models.  This particular BMS was chosen because we were able to run every load except the inverter through it, a configuration which allows the BMS to disconnect the DC loads when the battery is in a low state of charge (SOC).  In other words, it would cut power to the whole DC circuit array (distribution) once the SOC fell to a predetermined level, or when an individual battery cell voltage becomes critically low to the point where battery damage could occur (lithium batteries are expensive and they cannot be discharged all the way down to 0%).  This load-shedding does not disconnect any of the charging circuits, so the SOC can be recovered while the system is in low-charge shut-down mode.  Some other commercially-available BMSs disconnect both charging and discharging when the SOC falls to unacceptable levels, triggering a greater demand for human interface.  The Electrodacus is programmed to protect the battery from both overcharging and undercharging conditions.  There is no need for manual re-set buttons to remedy these conditions.

There are two charging inputs on the Electrodacus:
  • PV1 which accepts current from the alternator, shore power, and the propane generator
  • PV2 which accepts current from the 3 x 100 watt solar panel array 
Each of these routes charging current to the lithium battery (described below).  PV1 and PV2 are configured so that all inputs can be handled simultaneously; the BMS can safely handle up to approximately 100 amperes total input (hence the "100" in its model name).  In other words, solar charging can (and does) continue while alternator charging is also occurring, and/or shore power, and/or generator charging (!).  However, in practice, it is typically not necessary to stack charging sources.

21.  Lithium battery - Three GBS 12V (4-Cell) 100Ah LiFeMnPO4 cells were used deconstructed and reconfigured into a 300 AH battery.  The cells were rearranged to fit available space under our closet floor.  Here's a pic of how that was done:

22.  Electrical inverter - Xantrex Freedom Xi 2000 watt Pure Sine Wave Inverter was chosen for two reasons.  First, this model doesn't have a charger, and it was important that we separate our charging and discharging circuits for better battery management.  Secondly, this model had a built-in automatic transfer switch (ATS) which saved space in our tight build area.  Thirdly, the device's form factor meant that it could be positioned conveniently in an available space between the top of the lithium battery and the underside of the closet floor.  This inverter, when coupled with an EasyStart (described in Part 2), also allows us to run our 11,000 BTU Dometic roof air conditioner using the lithium battery alone for up to approximately 2.5 hours at a time (i.e., with neither generator nor shore power) before battery recharge is required.

23.  Positive busbar - The positive busbar allows the connection of multiple high-amperage wires to a single device with multiple terminals.  Without this device, the wires would instead need to be crimped in a way that did not reflect optimal design.

24.  Remote battery switch - This is a Blue Sea ML-RBS switch that isolates the inverter for safety reasons.  A short circuit developing in the inverter or in the high-amperage cables feeding it could cause a fire in the van.   This switch is connected to a pair of manual buttons on the control panel.  When we are done using the inverter, we isolate it by punching the "off" button and creating an open circuit at this point in the system.
Do you see those red and green punch buttons in the center of this control panel?  That's the remote battery switch.
25.  Shunt - The shunt is a 50 milliohm resistor.  The BMS reads the voltage drop across this resistor to calculate how much current is being used by the inverter.  All other loads go through the BMS itself, so it already "knows" how much current is being consumed for the other van circuits.  However, the external load from the inverter does not go through the BMS, so this device is needed.

26.  Negative busbar - This is where the chassis is tied to the negative terminal and return legs of all the major loads.  The negative busbar is tied to the chassis in a location behind the black water tank, under the cabinetry.

27.  Chassis ground - My husband describes the chassis ground as "the pool of electrons for all circuits".  The alternator, chassis battery, house battery, and all loads directly or indirectly connect to a common ground.  A ground is the means by which electricity is able to complete its journey and get back to the current source.

For those of you who are still on the steepest portion of the electrical learning curve (as I am), I highly recommend this webinar which has been reproduced as an unlisted YouTube video below, especially for understanding issues of grounding (earthing) and electrocution generally (HT this Sprinter Forum thread).  The video describes on-water mobile scenarios (boats), but similar principles hold true with on-land mobile vehicles (vans and RVs).  The person who presents the information is a parent who lost a young child to electrocution.  He was not a technician, but rather learned electrical engineering after his personal tragedy.  He uses clear lay language to describe complex constructs as a result.

The direct link below has the video continuing from around the 1 hour 13 minute mark, where the presenter is talking about electricity getting back to its source.  But IMHO, the entire video is worth your time, so I've embedded the full video below the timed link.  There are a lot of valuable lessons in it.