E350/450 Cab-Chassis w/ Composite Box Body - Feedback Requested

[luthj]

For reference a bare box with subframe, installed (no boxes or bumper) is about 57k. I priced out designing and ordering a box from a couple suppliers, once combined with materials, and needing to hire help for assembly (plus rent a small shop space fora bout 3-5 weeks for assembly and subframe), I could save maybe 20k. Though that doesn't count my time.

The recent inflation hurts, but the only other option was something used. Which is typically half finished projects, or older high time units. I could have gone with something like a Revel or similar. By the time I finished fixing the cabinetry, and upgrading the systems to my spec. Well, the cost savings was nil.

 

[rruff]

I'm sure I can probably save some money by diy a bunch of it. Given a14 ft box, I would need a bit more than just some poly isolators based on my math.

Can do 3 or 4 point pivoting, and spread the load out much better than single point bushings.

Since you probably want your camper and cab attached, a "3 point" arrangement with the front "fixed" would be best. That's how mine is. Space the front ones wide, and the rest would be on a centerline, so you'd need to bridge across the frame rails for those. I'm using Energy Suspension universal isolators (soft compound) and they are ~$20 each, and I'd recommend a max of ~400 lbs per. You can have multiples on each bridge member, but they need to be on a lengthwise centerline.

Sorry about this... I tried to post a link to my post, but it insists on embedding it for some reason...

Post in thread 'pivoting frames and mounting campers'

Nov 28, 2025

Interesting concept - do you have any photos?

This will have to do for now. Basically where you want pivoting to occur the isolators need to be in a line. Can do 3 point or 4 point easily enough. These are the soft Energy Suspension universal body mount bushings, cost ~$20 each now. Though I was told these would take a static load of 800 lbs each, that might be optimistic.

• rruff

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I don't know the details on how GT make the floor of their box... but TC uses thick pultruded square fiberglass tubes embedded in their floors at attachment points, and those would be plenty strong.

Totally understand if you just want GT to make all of it and not think about it. IME... I end up regretting that... because it turns out the fabricator I counted on to do the thinking, really didn't...

As far as the overhang goes I'm aware that it will produce limitations. But that's the trade-off I need to make in order to have something that I can full-time in with a child, and a reasonable level of comfort. I don't do hardcore wheeling, and really avoid true 4x4 routes most of the time. But decent ground clearance and the ability to drive out of the occasional screw up are important. If I really need more departure anangle, I'll uprate to 37 or 38in tires. Currently planning on 34/35" singles.

Longer wheelbase? 176 vs 158 would help a lot.

Your info posted at #4 doesn't change the overhang for the wheelbase, and the load height is surely wrong. Do you have an estimate of what you camper floor height will be above the ground?

Did some weight distribution math, looks like my planned 14ft box will just work weight wise. This includes the weight of a 4x4 conversion, and 34" wheels and tires, plus water, food, passengers etc. Load range F tire is good for 7940lb, so there is a bit of margin. I would like a touch more weight on the front axle, but there isn't much to be done with a 158"WB and a longer box.

View attachment 899054

That seems off, even with a 158" wheelbase, unless there is a lot of heavy stuff behind the rear axle. The chassis is very biased to the front, and at the camper floor you have ~100" in front of the rear axle, and 69" behind.

 

[rruff]

^How much is the box alone, and do they assemble it?

 

[luthj]

^How much is the box alone, and do they assemble it?

That is turnkey, fully assembled. No doors and windows at that price of course. Skirts or boxes are also extra.

I considered a longer wheelbase. But the sacrifice in turning radius was a more than I was willing to accept.

I think its also worth pointing out, that the storage boxes in the sketch I posted are mounted a bit higher than a typical setup. In the render below you can see that they hang down less than 6" below the frame. Note that those are larger tires than I intend to run. Overall departure angle isn't atrocious.



As much as I would like to do all the work myself, and avoid some of the pitfalls of having someone else do it. The reality is I don't have 2+ years to spend building a rig out. Of course money is in fact an object as well. I need to choose where to save my labor, and fabricating a box and subframe is a pretty good place to save. I can and will do the interior fitout, all the electrical, plumbing, windows, doors etc.

 

[luthj]

Your info posted at #4 doesn't change the overhang for the wheelbase, and the load height is surely wrong. Do you have an estimate of what you camper floor height will be above the ground?

I do, but not in front of me currently. It will probably be higher than I want, but.. trade offs! Lift will be 6" over stock approximately. Plus the extra height from Tire diameter increase.

That seems off, even with a 158" wheelbase, unless there is a lot of heavy stuff behind the rear axle. The chassis is very biased to the front, and at the camper floor you have ~100" in front of the rear axle, and 69" behind.

I have a 75-100gal fresh tank located just above the rear axle. The longer rear overhang and the "garage" being back there biases the weight rearward as well. Add an AC unit and spare tire to the rear wall to round it out. My math was based on the reported curb axle weights, COG of the box and contents, and the estimated 4x4 bits. I do basic COG calcs for aircraft mods on occasion, so unless my inputs are wrong, I am fairly certain the math itself is right.

My planned layout is fairly light up front, mostly due to a front entry and third seat being located there.

 

[rruff]

I do, but not in front of me currently. It will probably be higher than I want, but.. trade offs! Lift will be 6" over stock approximately. Plus the extra height from Tire diameter increase.

Plus subframe and room for it to pivot.