C5500 TopKick 4x4 Crew Cab Build


C5500 (now Int. 7400) 4x4 Crew Cab Build

New member here. This group has inspired me to start a custom build. After six years of trying to make a FourWinds 39C Funmover do things it was never meant to do, I found a good deal on a barely-used 2006 C5500 Topkick 4x4 Crew Cab chassis:

A typical journey for us is 200-300 miles on the highway, then 5-20 miles of dirt. I want something significantly shorter and lighter than the FunMover (33K lbs and 41 ft), as well as something that can deal with some rough roads in the west. Our primary needs are 1) good bathroom, 2) decent galley, 3) sleeping quarters for 2-10, 4) bomber. I've decided I'd rather hook up a trailer when I need extra gear/sleeping capacity than always have 40 ft. of vehicle around me. Here's one of my first sketches:

It's basically a 17x8x8 box with a 5' cabover. Having dealt with slide-outs in several RVs over the years, I'm thinking about having a simple "push-out" room that can be rolled out onto a liftgate like we have on the FunMover. One of the challenges to expanding/multi-function interior spaces is furniture and floor coverings, so I'd love to hear any ideas.

I was totally impressed by Jay Shapiro's build. This will be a much more modest venture, but I'd like to make a decent attempt at incorporating as much solar, wind, and bio-fuel into the project. I'm trying to get educated on PV, wind, batteries, etc. Has anyone on the board ever done solar thermal for radiant?

I've talked to several body builders and a couple of structural panel manufacturers. I'd love to hear about your experiences with structural panels for walls and floors, vs. more traditional tube/stud framing.

I'll post more design pics later, but feel free to chime in.
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That is very cool! I feel your pain with my current class C (which is not in the same league as your Funmover) and 3 young ones.

If 17' is the unexpanded cabin size, might you consider lengthening the wheel base? I don't see sleeping 10 people as is. Let down bunks over sofa or Pop-top might help.

If the slide out runs onto a lift gate, a bifold one could act like a bike carrier at the same time with little length penalty when not in use. You might be bumping into the Gvw limits if your not careful with gate, hydraulics, etc...

I'm subscribed for this one.


Expedition Leader
I'm pleased to see this, too. In terms of practicality and value, I always thought the last generation of the C/K 4500 and 5500 were as good as it got for a potential overland platform and I was sorry to see them stop production.

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Hill Bill E.

Oath Keeper
Awsome plan! I really like the rear slide out. Nice thing is, it looks like you can use the galley/etc without having to deploy the slider!

Great for that 30 minute 'lunch stop' on the trail!:coffeedrink:

Capt Eddie

I have been in your shoes. You need to look at this build from two directions. One is to buy a truck camper big enough to do what you want. And start using it in about 7 days. Or plan and design and build for a year. Or more. Just think of all the missed times. Many of the experts on the site will admit that most people spend all their time planning for the perfect rig that never happens. Buy a camper and start camping is my thought. You have the perfect truck for the biggest lance camper. Add some aluminum boxes and your can be camping next week end. OH don't forget that your custom build is going to cost you 3x or 4x as much as the BIGGEST Lance.


But building stuff is half the fun!

I've never let building something get in the way of our adventures. We've got plenty of things to do with the rig and other gear we've got- living in Utah makes that easy. And it's fun to see something of your own ambition or creative process become reality, even if it takes longer and costs more (which has NOT been my experience with past projects).

So here's a look at the under-box layout so far:

First, the chassis will be lengthened to a 229" WB, per the GM upfitters specifications for a box this size.

As for a torsion-free mount, the body building I'm probably going to work with has done a bunch of 4x4 and 6x6 commercial rigs. They use something similar to the U-bolt w/springs rather than a 4-point mount. Their rigs have a good track record on the stiffer GM chassis. I'll try to get some photos or a drawing.

To keep the CG low and the weight where it should be, all the tanks and genset will be mounted as shown, which will also allow access/removal for inspection, service, and repair (lesson learned from owning a commercial RV for 6 years). That will leave the rear under-box area free for storage compartments (including an 8" high pass-through for a table, shovel, jacks, etc.).

I still need to think about a battery configuration (how many, where).

I'm also looking at the EcoJohn incinerators. The foot print is too big for the diesel unit, but since I'll have propane on-board anyway, I might be able to find a way to get the WC-5 on-board (the flue stack also presents some configuration challenges). I emailed the manufacturer about integrating a heat-exchanger in the unit, which, when coupled with a small diesel radiant water heater, could make it a lot justifiable.


Director of Adventure Management Operations
If you feel the nee dot donate your old RV to a good home..I am always available...lol


I know this has been beaten to death a hundred times over on this forum alone, but, are you going to keep the dualies? I never thought it a problem until I picked up a softball sized rock last month. Disturbing in that I didn't know about it until I got back on tarmac. Could have turned out worse if I had driven twenty miles in the dirt. Speaking of, you have yet to place your spare(s) with your rather prodigous CAD skills.

Just a thought, I am utilizing a composting toilet ala Ecoroamer and thousands of maritime folk. Most people seem really happy. Installation includes screwing the unit down to the floor. Super simple, no fuel, no tanks. It might simplify fuels if you already have diesel for the Duramax(?) and a diesel generator and can handle cooking with catalytic diesel.

Others are more familiar than me, but, mucho AGM batteries are needed if you want to run AC in your Utah environs. You probably have plenty of experience with the Funmover in this regard and may not be neccessary if you plan for plentiful ventilation. I am interested in your past use of AC in the southwest.


I've been trying to reseach the super-single topic as much as possible. While I've never had an issue with the dualies on the Funmover picking up or throwing rocks, it seems to be a common problem. I'd love to hear first hand opinions/experiences.

Thanks for the composting thought. I'll check that out.

The plan is to have an AC unit. I can count on one hand the number of times we've used the AC in the FunMover during the day. When the sun is up, we're usually away from camp. We go south in the winter, spring and fall, and stay in the higher elevations during the summer. But it's something I'd like to have. Has anybody ever used one of these:


One of my neighbors has a company that makes light, strong masts for the military for communications, solar panels, and even small wind turbines. He said he could set me up with a blem for cheap. Our general area of travel has great insolation values for solar, and when the sun goes down temperature gradients tend to kick up a steady breeze, so I'm hoping to find a way to keep the diesel generator off as much as possible.


New member
In my experience Dualies do pick-up rocks. That is why I carry a Large hammer and also an air hose to reinflate the tire(s). I have had large rocks wedge themselves between the sidewalls, you obviously need to get them out before hitting the Highway. This has been with a Freightliner with 22.5" rubber and B-Trains. I can not speak for smaller dualies but I imagine they have the same problems.
As for Super Singles, on my work truck No thanks! But on a expo truck maybe, just carry a spare. Last I checked not many people stock Supers, especially at 11:00pm.


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I would definitely build the box, we built a deck complete with under body crossover storage, aux fuel tanks, and just finished installing all the custom built aluminum storage boxes to fill in the sides of the unit. It is a very big camper so the height came in at 13 feet, a little on the tall side, it doesn't drive as tall as it looks, it actually handles the load well, but it is quite tall. The 5.5' frame to top of cab is a big reason for that issue so it would be best to do a custom build on that platform. http://www.expeditionportal.com/forum/showthread.php?t=25494&page=23 pics are here


I would definitely build the box, we built a deck complete with under body crossover storage, aux fuel tanks, and just finished installing all the custom built aluminum storage boxes to fill in the sides of the unit. It is a very big camper so the height came in at 13 feet, a little on the tall side, it doesn't drive as tall as it looks, it actually handles the load well, but it is quite tall. The 5.5' frame to top of cab is a big reason for that issue so it would be best to do a custom build on that platform. http://www.expeditionportal.com/forum/showthread.php?t=25494&page=23 pics are here
Just met with the upfitter this afternoon to go through the scope of work on the body build. Everything seems to be coming together on the design/budget side. I'll pick up the chassis next week and the upfitter will start the wheelbase extension and body build.

Jeep, thanks for the link. The spring mounts on that page in the thread look almost exactly like what he's recommending. This particular upfitter has built a lot of "dynamite" trucks (didn't know there was a category for that particular upfit!). How are you liking your Topkick?

The box will still be tall, just about 12 feet, depending on the tires. I'm trying to keep the CG as low as possible and keep the weight distribution in line with the GMC upfitter recommendations. I'm going to swap the standard fuel tank for two 50 gallon tanks in the forward steps, then use the two crew steps for battery boxes. I've been able to keep all the heavy stuff below the floor level and in front of the rear wheels. I should know by the end of the week what whole rig will weigh with full tanks.

I'm still curious to hear if anybody has had experience with either the diesel or the propane EcoJohn WC incinerators. I've got room for a WC 5 (propane only), but only if I can work with the flue placement a bit. I've exchanged a few emails with the owner about a smaller footprint diesel and integrating a heat exchanger for hydronics, but the dialogue is pretty slow.

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I built that truck for a friend of mine and so far he is happy with it. I am building mine on a Ford F-700 4x4 and like you I am building the camper.


Side panels, roof, floor, frame.......

The chassis goes to the upfitter this week. They're going extend the wheelbase, put airbags under the cab, and install two 50 gal. step tanks and two step battery boxes. Then the wheel shop will put on the 22.5 rims and tires. I'm sticking with the dualies for now.

I'm trying to make a final decision on the camper box make-up. As much as I'd like to use high-tech panels, it's a royal pain to acquire the materials. I've made inquiries into NidaCore, RhinoCore, and MonoPan, in addition to SingPanels and CladFoam (Fiber-Tech).

MonoPan is pretty cool stuff, but it's very pricey and hard to get in the US. Fiber-Tech is clearly the easiest to work with on this sort of thing, but it's still pricey and heavy, but within my tolerances. Has anybody every looked into the Sing panels besides me? I had a phone conversation with the inventor, Peter Sing, and he thinks his stuff would be unbeatable. I'm still waiting for pricing on RhinoCore and NidaCore. It doesn't seem like anybody is in a hurry to sell any of this stuff for a "one-up" build.