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

[ExpoMike]

L brackets made of 6061 1/4in 3x3 angle connect the tubing using BOM Rivets. Each rivet requires ~6000lb clamping force to shear in place, and has a tensile strength of 3250lbf and shear strength of 5100lbf. This construction technique has many advantages over welding, but it does however add cost and require a specialty tool for install. I got the idea for this construction technique from XVENTURE trailers, who have a proven track record of zero failures being used for overloading and as heavily abused military trailers. When installing the BOM Rivets, I use a generous portion of lancote to prevent galvanic corrosion. While it worked great for this purpose, the Lancote got over all my tools and was a mess to clean. I am switching to a chromate primer and doing a wet install (got this technique from aviation manufacturing). This should make less of a mess and not require clean-up before painting.

That is looking great! Would you have any interest in renting out the install tool? I could see using this construction method but for a one time build, hard to justify the cost.

 

[PathNotTaken]

That is looking great! Would you have any interest in renting out the install tool? I could see using this construction method but for a one time build, hard to justify the cost.

I would, however I don't own the tool myself and was able to find someone to borrow it from. However, it was a one time situation so I'm really no help here. The tool cost is really not ideal. Once I'm finished with the subframe I will add some thoughts on this construction technique vs having just welded the thing, I really don't think welding is a bad option if you are confident in your welds. I'm going to have to weld a bunch of other stuff anyways

 

[PathNotTaken]

Looks great. Love the photos. Please elaborate on the description about the Chromate primer and wet install

Essentially just getting fastener wet with paint before install. I wasn't able to find a can in order to dip, so I just sprayed a healthy amount of paint and install the fastener with the paint still wet. The Primer I used is Zinc Green 5605 Marpro. If you get the same primer, read up on it and use maximum PPE. Zinc Chromate is very harmful. My understanding is it isn't the same formula it used to be, but still very toxic.

 

[PathNotTaken]

Here is my subframe X-Brace before painting and after install. Came in at only 29LB and should increase the strength in the rear significantly.

 

[PathNotTaken]

Getting ready to order the metal to make my box 3D. Planning on bent 5052 Sheet to form an angle, with flanges ~2.75in except for the top, which requires around 5in for pop top clearance.

The question I am faced with now is what thickness to go with. I've planned .125in this whole time, but am considering .100 as I could save about 20lb across the whole structure. Not a ton, and maybe not worth the risk, but this would give me more weight allowance for other parts of the build. I really don't think the exo is providing that much structure at the end of the day, its job is to align and bond panels together.

I've seen a few builds with 3/16, and most if not all say they wish they went with 1/8 instead. The only thinner build I know is ambition strikes, as they used .080. Thoughts?

 

[hidn45]

Love the spec you've laid out, & the build is looking great so far!

To a certain extent your corner selection would be guided by the panels you are putting together. As you mentioned, a habitat assembled with structural composite panels wouldn't necessarily need a frame at all. At that point the determining factor for the corners is what sort of "trouble" you're planning to get into relative to the amount of corner protection you feel you need. If weight is a primary consideration, then the slight loss of protection in going with .100 vs. the 1/8" isn't really that significant, & the pieces will be marginally easier to form. Some good discussion on edge protection here: https://forum.expeditionportal.com/threads/custom-extrusions-for-frp-panels.229840/#post-2985692

Keep in mind also the attachment method you are planning, in case a corner is damaged to the point that you want to replace it. There's also the issue of differential expansion, which can usually be accommodated by the thickness of your adhesive.

So, what manner of panel are you planning to put together (or did I miss that somewhere?).

 

[PathNotTaken]

Love the spec you've laid out, & the build is looking great so far!

To a certain extent your corner selection would be guided by the panels you are putting together. As you mentioned, a habitat assembled with structural composite panels wouldn't necessarily need a frame at all. At that point the determining factor for the corners is what sort of "trouble" you're planning to get into relative to the amount of corner protection you feel you need. If weight is a primary consideration, then the slight loss of protection in going with .100 vs. the 1/8" isn't really that significant, & the pieces will be marginally easier to form. Some good discussion on edge protection here: https://forum.expeditionportal.com/threads/custom-extrusions-for-frp-panels.229840/#post-2985692

Keep in mind also the attachment method you are planning, in case a corner is damaged to the point that you want to replace it. There's also the issue of differential expansion, which can usually be accommodated by the thickness of your adhesive.

So, what manner of panel are you planning to put together (or did I miss that somewhere?).

Thanks for the reply and link to that thread. I didn’t come across it in my research, but it had exactly the info I was looking for!

Dang, reading that and your response is making me want to go lighter with the .100 Aluminum. Slight cost savings (not a big deal) and lighter is a huge plus. 20lb isn’t a ton, but it gives me a weight allowance to reinforce later in other more effective ways. Specifically my pop top with the open roof.

My plan is to make an aluminum exo with the bent angle pieces (welded together) and then adhere panels 1.625in thick (1/16 FRP and 1.5in core) to that from the inside.

 

[hidn45]

That sounds like a plan! I like the 4x4 cutaway as a platform as well - a great compromise between a conventional truck & the much more compact but unicorn 4x4 Isuzu/ Fuso base. Looking forward to seeing it come together.

Personally, I'm still trying to come up with an overall layout that pleases The Little Woman without needing a Peterbilt to haul it around. But I've got a little time - we aren't retiring for a few years yet...

Build on! 🍿

 

[simple]

What were your thoughts regarding building out a subframe and box vs starting with a cube van?

 

[PathNotTaken]

What were your thoughts regarding building out a subframe and box vs starting with a cube van?

A lot of reasons! I'll name some that come to mind in no particular order...

• low quality construction not intended or designed to be used in such condition (frame flex, most of these are mounted poorly)
• Requires additional insulation and inner wall structure unlike composite panels
• most are pretty heavy for their size, especially when you consider insulation/inner wall
• hard to find used cube vans in good condition that aren't beat, new ones the boxes are relatively expensive
• most (maybe all?) have large rear openings/doors
• none are close to the dimensions I wanted (narrow as the cab, short height, short box)

With all this said, I still think a cube van is a really good option for a lot of people if you're able to find one to your spec.

 

[PathNotTaken]

Other then wrapping up a couple loose ends, the subframe is complete. I've been working on a few odds and ends like relocation the driver seat further back, grey water tank mounting, aux gas tank mounting, evap canister relocation, heat shields and exhaust wrap, and future planning for the build.

I just received the bent metal frame pieces from the shop and am really happy with how they turned out. All of the metal to make it 3d dimensions came in at about $300, and $250 to get it bent to shape.

I'm also really happy I went with .100. Feeling it in person really confirmed that it's more than adequate for its job of holding the panels together! I saved about 20lb over going with .125 and 60lb over the the 3/16 I was originally considering! This might just be the first decision I've made thus far where I choose the lighter option

 

[PathNotTaken]

Next Steps are to get the 3D frame, rear bumper, and wheel wells tacked in place.

Deciding the size of the wheel wells has been a pain, Ford gives guidance in the BLBB on how big they should be for stock tire size, but I'm pretty sure they are being very generous on the size. I'll have to measure a passenger van.

 

[PathNotTaken]

Super excited to say the camper is now 3D! Was really cool getting to see the space come to life. as it sits now, it only extends about 5in above the cab. it will extend another 9in for the pop when I eventually get to that. This thing is really taking up the entirety of my one car garage now.

the 3D pieces are made of bent .100 5052 Aluminum. My next steps are to frame out the wheel wells, rear bumper, and sides. Then tie up all the loose ends before it's permanently mounted.

As for permanently mounting it, I think I am going to go adhesive only. I was initially planning on doing adhesive + rivets, but the rivets are adding a marginal amount of strength and will make the joint less flexible. I estimate I could have about 350 linear inches of glue surface, so ~152,000lb tensile strength. The strongest countersink rivets I'm seeing are ~1200lb, and I think I'd only be able to fit 15 or so. The strength additional seems minimal, and ruining the flexibility of the joint is not worth it. While the rivets do also act as a clamp, I think I will be fine setting up a jig to apply slight pressure to keep things aligned. The habitat will also be bolted via the body mounts so that will preset the perfect gap.

 

[PathNotTaken]

Turns out I was planning to make my wheel wells way too tall, and already made them too wide. Ford provided guidance in their BLBB for how big the wheel wells need to be. I contacted them and was told this plans for "worst case with factory tire size". So, I used this size to determine the height (and width) of the wheel well based on my planned tire size. This was going to be about 17in above the frame.

Looking at other builders, they make the wheel wells pretty small, and haven't had issues fitting big tires. turns out that when fully flexed out, the rear axle is nowhere near the bump stops. I mean like still 6inch or so away. I confirmed this with with @UjointoffroadCO when Justin lifted his on the forklift until opposing corner tire was off the ground. He still had 6in of clearance between the top of his stuffed 37 and the wheel well. I believe the shock was bottoming out first? Still doesn't make a lot of sense to me.

Anyways, I now am going to shrink my wheel well by 10inches in width at the height of the subframe, and only need to make it 6in tall or so. My body mounts were designed to place the wheel well edges at a particular distance, and now get in the way of be placing another bar where I need it, so I'll need to work around that.

 

[rruff]

The bump stop should be the thing limiting movement unless the load is quite light for your springs, but you can probably extrapolate to a fully loaded condition well enough. Do you have photos or videos of the Ujoint test?

I have ~7" of clearance between the top of my tire and the bottom of my camper and haven't managed to touch yet. I have airbags instead of bumpstops, though.