E350 Cutaway 4x4 w/ DIY Pop-Top Composite Camper Box (Build Thread)

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Officially starting the build thread for our E350 Cutaway 4x4 w/ DIY Pop-Top Composite Camper Box!

First, why a new build?
The initial plan (many years ago) was to convert a high roof Transit Van. The cost of that wasn’t an option at the time, so we ended up with an Overland-setup SUV to hold us over until it was. The idea was it would still be daily drivable (only had a motorcycle at the time) yet get us out there.
We ended up finding a really good deal on 2013 Nissan Xterra. The previous owner took extremely good care of and took care of many expensive mods (air lockers, bumpers, sliders, skids, awning, and much more). It was ready to go as is, and we took it on an awesome trip. Soon after it was time to make it out own and build it out. Over the course of a year we added an interior drawer/kitchen system, rooftop tent, custom table, water tank, battery setup/fridge, and many other “living accommodations”.



We’ve since taken it on many insane trips, traveling across the Western US, Mexico, and Canada. It’s been the dream vehicle and has gotten us to many places we never imagined possible. With that said, it completely crushed the dream of the high roof van. It was simply not capable enough of a vehicle for the places we go, and no amount of modifications could change that. With that said, while the Xterra was a great vehicle, after 1-2months of traveling (and trying to work remotely) the comforts just weren’t enough. I have nothing but admiration for those who can last longer out of an SUV as you truly are another breed. And with this, the search for another vehicle for our planned fulltime travel began!

 

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Vehicle Considerations:
Here is a high level overview of our must-haves:

• Interior sleeping (stealth option also, ie no pop top raised)
• A configuration that allows me to stand up completely and comfortably
• An comfortable indoor space for all weather situations (rain, snow, -30º to 80ºF ish)
• Room for two to work comfortably on laptops
• Ability to carry significant resources for extended off-grid travel (fuel, water, food)
• As fuel efficient as possible (lol)
• Off-road capable (I’ll expand on this and what it means to us)

As for off-road capable, this means a few things. The most important and often missed point imo is the overall size. IMO the biggest limitation for where I go is physical size. A Unimog-type vehicle may be a beast "off-road" but "off-roading" anywhere I've ever been is traveling on bad roads, not just across barren land. A large vehicle simply doesn't fit and defeats the intended purpose. Overall length cannot be any longer than mid-size to small full size truck. Width also cannot be any more than a full-size. Weight needs to be at an absolute minimum to maintain low weight/tire footprint and overall capability. Height also needs to be absolute minimum, which makes a pop top a must. CG needs to be very low, as much suspension travel as possible, robust 4wd, reliable serviceable system.

With that said, the major contenders were a full-size pickup, a gladiator/wrangler build like WabiSabi (@LostInTheWorld ), and the E350. I still think WabiSabi's build is unparalleled in its segment, but it just wasn’t quite large enough for the requirement of stealth sleeping, room for two to work, and resource carrying capability for our travel. And thus, we bought an E350 cutaway. First, some interesting specs that sold me over:

 

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Cool E350 Composite Camper Specs:

• Overall Width: 80in (Dana 60, same as full-size)
• Overall Length (with 10ft habitat): 212in (6in shorter than a jeep gladiator!)
• Wheelbase: 137in (Same as jeep gladiator)
• Insanely good approach angle, reasonable breakover, and good departure
• 16in of front wheel travel with @ujoint @UjointoffroadCO kit
• 5,000lb+ payload capacity
• Room for 37s
• Robust 4wd, axle, suspension system capable of handling the weight off-road. Easily serviceable.
• 325HP and 450ft-lb torque (significantly detuned from factory)
• Estimated completed Dry Weight of 7350lb (I’m sure it will end up more, but this is calculated using a spread sheet of every building material/item)

 

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Interior Plans:
I plan to go into this more in depth later, but for now a quick overview:

There will be a full roof pop top, and 10ft long of interior living space. The bed will go front to back, which is the only option given my height. This means the bed will be almost the width of a California king bed! The couch will be sitting height and be a secondary smaller bed for stealth sleeping when the pop top is down. There will be 900ah of lithium, induction cooktop, hidden shower, and I’m sure a million other things I’m missing. I made a 1:1 scale mockup of the build 6 few months ago so we already got a good feel for the dimensions, and they’re perfect. felt much bigger than the model I had been staring at for over a year.

 

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Exterior Plans:
The basic plan for the exterior is to do a spring mounted aluminum subframe with a welded aluminum exoskeleton. DIY Composite panels will then be adhered to that. The pop top will then mount the aluminum skeleton and raise vertically.

 

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Next step will be finalizing the design on the spring mounts, one of the most important parts of the build IMO. I have the design pretty finished and will post about it soon! Once this is ready to go, I'll start constructing the subframe.

 

[WildernessSV]

Following. Sounds like an interesting build and some great, if challenging, parameters to work within. Will you be TIG welding the frame yourself? I would like to build out with an aluminum frame but nervous from all the comments of it being “weak” structurally, off road, over time.

 

[Bigly]

This would be my dream vehicle as well. Good luck with this build!

 

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Will you be TIG welding the frame yourself? I would like to build out with an aluminum frame but nervous from all the comments of it being “weak” structurally, off road, over time.

Current plan is to do a TIG welded aluminum frame, but I am also considering steel. I agree and am also nervous working with aluminum: This is currently the biggest decision I face. To preface, I am not a metallurgist or mechanical engineer, but here is my understanding:

1.) When you weld 6061 aluminum, your heat-affected zone from the weld loses strength, from roughly 42,000PSI to 27,000PSI. This effect is not nearly as drastic with steel.
2.) The fatigue behaviors of steel and aluminum are very different. Steel's loss of strength from fatigue eventually plateaus to a point at which no more strength degradation occurs. Aluminum on the other hand infinitely fatigues until its tensile is effectively 0. Now in the ~250,000mile life span of a vehicle, its not unreasonable to hit the point at which you're aluminum gives if you're structure is flexing from the cyclical load of offroad/onroad driving.

To counter #1, for my sake I'm just accepting the fact that whatever material thickness I choose of aluminum, I need to realize that my joints will be ~40% weaker. I've considered a bolt together system, but haven't came up with anything I like.
As for #2, I think the only solution is to make the structure strong enough that it isn't being fatigued under driving conditions. The thing I keep telling myself is by the time the composite floor is glued in, walls, and internal aluminum cabinetry, it's gonna be a pretty damn strong structure. It's not like the subframe has to be strong enough on its own.

With that said, if 2 years from now when bombing down a washboard road at 50mph my mind is worried about the aluminum welds/fatigue, steel may be the right choice despite the weight penalties and other complications it adds.

 

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Aluminum Weldless Subframe Construction Technique Consideration
Thought I should share a new subframe fastening technique I am considering as opposed to welding the aluminum. The company XVENTURE makes military trailers as well as overland trailers with this technique. Essentially you rivet together the subframe with L brackets and these extreme duty blind rivets. They have a good video showing the construction here. Since they make these for the military and have a long history of doing so with zero failures, the method is quite proven. This would allow me to use aluminum without welding, and near zero user error (aka my crap tig welding). I would still probably weld some less crucial joints along with the exoskeleton part since the joint strength isn't as important there. This does add cost ($1 per rivet, and ~$100 of aluminum bracketry), but I wouldn't consider the cost difference that drastic compared to welding. This will however make my cross brace placement different as the brackets would take up some space.

 

[rruff]

With that said, if 2 years from now when bombing down a washboard road at 50mph my mind is worried about the aluminum welds/fatigue, steel may be the right choice despite the weight penalties and other complications it adds.

You'll be able to make an aluminum structure that won't fatigue lighter than a steel structure that won't fatigue.

 

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Spring Mounted Subframe Design
I roughly measured the frame flex of the chassis at ~6in of vertical displacement, meaning the mount right behind the cab is 6in lower/higher than the rear mount on the opposite side. It's expected that the chassis will flex a lot without any box, as the frame is designed to be used with a box that is also providing rigidity. And the job of a spring system isn’t the same as a zero torsion 3/4 point pivot: it reduces the stress induced on the subframe by the chassis flex, it does not eliminate it. I decided on spring mounts vs a pivoting frame system for various reasons I outlined here. The E350 is also unique in that the cab is fixed to the box. This makes it extra important that the cab-habitat interface isn’t over stressed.

Here is a sketch of my subframe mount design:

The springs will be of varying length depending on which mount it is, with no spring for the first mount. I’m using the factory ford mounts since they offer a lot of travel as is (0.75in according to ford). It’s also the same connection the cab has with the frame, meaning the front of the habitat will move the same as the cab. Since the largest bolt I can fit in the factory mount is 1/2in, and the smallest inner diameter appropriate spring I could find is 0.75in, I designed a collar that will be welded to the washer to keep it in place. Other than that the only unique part is the secondary bushing. The reason for the additional Energy Suspension poly bushing is to act as a buffer when the frame separates and then slaps back down. The spring compresses as the chassis moved downward away from the habitat to flex, and the bolt becomes exposed between the chassis and subframe. Without this secondary bushing, there would be metal on metal contact when these come crashing down. It also lifts the subframe enough to clear the axle hump. With this said, this setup allows me 1.82in (46.2mm) of movement in my rearward mount. I should have all the parts here shortly to show a mockup of the actual parts.

 

[rruff]

I'm thinking you should have poly bushings on both sides of the subframe... at least that is how they come, in 2 parts.

Otherwise that looks ok to me for the rear part, but up next to the cab you'll want something stiffer, if your camper and cab are going to be attached.

How much travel does the spring have, and what is the rate?

 

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should have poly bushings on both sides of the subframe.

I was considering this, but I feel like theres already a lot of bushing in there! I'm thinking it won't matter since I have bushings on both sides of the frame already? This is also the way the factory ford mounts work if I just used them as is. Happy to be proved wrong just with already having 3 bushing it seems a lot to add another. I could always add a thin 1/4in pad.

but up next to the cab you'll want something stiffer, if your camper and cab are going to be attached.

The springs are only planned for the rearward mounts. the front mount is identical to the way the cab is mounted to the frame using factory ford bushings, except for the additional energy bushing. but the movement of that should be minimal since its high durometer. If its compressing to much I can always replace it with a stiffer material. TLDR the bushings should encourage movement at the same rate.

How much travel does the spring have, and what is the rate?

Travel/rate of the springs themselves varies, from 0.5in to 1.07in (not including additional 0.75in travel from ford bushing). Spring rate is in the region of 800-1250lb/in (14kg/mm-22kg/mm), not yet finalized. Build will be relatively light and I can always change them out later once near final structure/weight. Though I do think leaning towards too stiff is the best call, since too stiff = no flex happens, too soft = subframe bouncing!

 

[rruff]

I was considering this, but I feel like theres already a lot of bushing in there!

The universal ES bushings already come that way, with a top and bottom piece and an internal steel sleeve that takes a 1/2" bolt, made to fit it a particular size hole (think lower durometer ones are 1.25") in a 1/4" thick frame. I guess you were thinking of something else, and you are correct that they don't provide much vertical movement.

The Ford mounts must be sponge material of some kind if they will compress .75". I wonder if adding another one of those instead of the spring might be better...