Someone did what I am trying to do! Foamie cap / camper on a full sizer...

[rruff]

Here is something I put together for estimating panel costs and weights for a few different concepts. The lower ones with XPS core all use wood in the core as well. The layup shown is for one side; both sides are the same. When I did most of my build I got Ebond epoxy for < $30/gal (plus ~$15/gal shipping), but they recently increased their prices to $46/gal. It's still the cheapest I've found though.

 

[rruff]

The reason I suggested a flatbed was to make the build simple.

I agree. Since the OP has a very flexible C-channel frame, it's also good to have some flex between the main frame and flatbed, to keep stress away from the camper.

 

[jingram]

The reason I suggested a flatbed was to make the build simple. An aluminum flat bed would be lighter than the original bed/tailgate. You could also do a 7x7 ft flatbed, it would stick out only 3" past the cab and probably not go past the rear bumper. You don't have to use a $12,000 Austraiian imported bed, the 7x8 1/2 Protec flatbed cost me $3500.

When you build the box, everything is straight and square. It would also fit any future truck you bought. Put a plywood floor in it and you could remove it from the flatbed. You would also have a huge sleep bed laying cross-ways. You get a 7x7 floor, instead of 4x6.

It is also flexible on the man door location, having a door on the back bumper is a pain and usually dirty/dusty. Side hatches can then be used.

Where on earth did you get a Protec flatbed for $3500? I’m seeing them for 10K on average.

 

[dbhost]

I agree. Since the OP has a very flexible C-channel frame, it's also good to have some flex between the main frame and flatbed, to keep stress away from the camper.

I am building on an '04 F150, which has a fully boxed frame.

 

[rruff]

I am building on an '04 F150, which has a fully boxed frame.

I didn't know that! I thought they went to boxed more recently, but I guess that was just the Superdutys. Sorry for the misinformation.

 

[Zuber]

Where on earth did you get a Protec flatbed for $3500? I’m seeing them for 10K on average.

1. live only 70 miles from the factory
2. buy it 4 years ago before inflation
3. don't pay for any extras, like removing things.