GMC Topkick 4x4 Expedition Camper Build

Fuel tank

The original tank is between the rails just behind the new brackets; you can see it in the pic.
I've been painting the brackets, and the tank, using POR 15. Total pain to clean rust off tank wirh wire brush in mini grinder. But the "rust killer" that POR supplies seems to do a good job. I'm irritated to find that POR won't stand UV, so the tank will need another coat to protect the POR ????
Transfer case wiring

My donor truck was a 2007 4WD. The "new" truck is a 2003.
The NP273c transfer case is "divorced", and also electric operation with a switch on the dash. However, there are 5 wires from the transfer case, and, would you believe 10 wires on the switch !! I don't think I'll ever figure out how to wire this into the new truck - GMC didn't launch the 4WD truck until 2005.
So I'm fabbing up a lever to go on the xfer case, using a piece of steel cut from a leaf spring, so it's nice and hard to go over the very small shaft coming out of the case. It's at a machine shop now getting the slot cut. I'll post pics later.
Then I need to fab the linking, and cut a hole in the floor....
Do you know the measurement of the width of the frame rails outside to outside?
I’m trying to see how it compares to the width of a ford e350 frame.
It’s may be narrower which seems odd to me.
Britboaters, where did you go to find a wrecked Topkick? Just for fun, it would be sweet to find a wrecked 4x4 kodiak or topkick to convert my own rig to 4x4.
cjken - frame rails are standard US truck (Freightliner, etc) 33.5 outside from memory.

Ross - might be a source.

Very slow progress on my rig, I'll post some picks when I get it in the sun.
I built a 4"x2" subframe, mounted to the chassis on 3 points, using Freightliner class 8 front spring bushings, about 4" long and 2.25" diameter, with a 20 mm bolt hole.
I took the subframe to Complete Bodies, just south of Atlanta and they're going to build me a standard box truck box directly on my subframe. I went this direction so I can have a nice new box, really well built, to my specs, with a good chassis mounting system. It will be fully waterproof, with a very robust exterior, really quite light weight, and an excellent starting point for fitting out.
14' 6" long, 8' wide, 85" headroom inside. There will also be an 36" attick over the cab for storage or a single bed.
The box will have a hardwood floor which we intend to varnish, should look good. The structure is 1" thick "Z channel", clad with white painted aluminum (or aluminium). Roof is also aluminum.
They will be cutting my window & door openings as well.
My intent is to fir out the framing using 1 5/8" (1.625") x 20 ga wall studs to give me almost 3" wall thickness, run all the wiring, etc before filling with either styrofoam, or maybe spray insulation.
Fresh water tanks, 2 x 30 gal, are mounted between the frame rails, behind the axle.
I'm planning a pretty large solar system, so 2 boxes mounted on rails also behind the axle to each hold 4 golf cart sized batteries. The boxes slide out on rails I built for maintenance, etc.
Will hopefully have the box soon, and then my wife ("trouble & strife") will have something to really get interested in. I'll put the box on the floor while fitting it out, then figure out how to lift it up onto the truck later. The bare box will be about 2,200 lbs, and kitted out, less than 3,500 I hope.
I've got the body.
We ordered a standard box truck body 14ft 6" Body pick up 1 reduce.jpg Body pick up 2 reduce.jpg Body pick up 3 reduce.jpg long, x 8ft wide, x 7 ft inside dimensions. We had them install a standard RV door and delete the rear door, as we intend to close it in.
This will be the basis of the camper build. The floor is laminated hardwood, so once varnished should look pretty good and be very robust.
I built a subframe 1st, and mounted this to the truck frame using 3 Freightliner front suspension bushings. The body was then built directly on this subframe.
The walls are aluminum with 1" thick stiffeners. We'll stiffen them up with 1 5/8" thick drywall studs to give an overall wall thickness of about 2 3/4". Once all wiring and plumbing is done, we'll fill it with insulation.
So we got it in the shop today with the help of some good buddies, a skidsteer and a mini excavator (and a tractor). I'll post some pics of that fun.
Next job is to sand and varnish the floor
Front body mounts reduce.jpg Left battery box & bumper reduce.jpg Right battery box reduce.jpg

Top photo shows transfer case mounted further back than stock - about the middle of the 2 axles. Also the front mounts for the body. Bottom photo shows both battery boxes, for 4 - golf cart size batteries each. They're on rails so they slide out for access. The big nuts are to hold the boxes in place. I need to make lids for the boxes at some stage as well. Also the frame crossmember was boxed in, and one the rear mounts for the body is shown.
The rear bumper (8 x 4 x 3/16 box) is hopefully stout enough to mount a lift for a bike and spare wheel. Lots of 1/2" grade 5 bolts holding it in place.
One 30 gallon water tank will go between the battery boxes, and a second will go behing the rear axle.
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Looks awesome. So no pass through from cab to box?
What’s the wheelbase of your c4500?
The box looks like a perfect size. Nice and roomy.
Thanks guys.
No pass thru yet....... The front of the box is plywood with a fibreglass surface - I'll cut the pass thru later. Truck cab will be a bit more difficult.
WB is 188".
One thing I need fairly soon is an extractor fan / skylight. All the ones I've seen were really light and flimsy - horrible.
Any ideas please ?
Not much light.
Mostly happy it works great to vent heat out the top. It started making an annoying squeaking sound recently. I have not had time to investigate the sound.