Frank,
I'm in the same boat as Alex. Our '01 Dodge 2500 factory bed has taken it in the shorts over time. Remember the bed is held on by four, 3/8's inch bolts that do spread the shear factor over a rather wide area. At least they're grade 8, but I can't say much about the thin metal tabs that they bolt onto.
That being said, the R-pass side bolt has pulled through it's flimsy little mooring a couple times allowing the TC and bed to rock and twist. That could be scary in a very high wind or axle twisting event, kind of like this;
It's the twisting of the frame over time that caused this. Fords by design have the most flexy frames, at least until the last few years, which I think has been a woe for Alex with his '07.
Currently I'm looking around for an aftermarket pickup bed specifically made for truck campers. Here is the closeset I've been able to find, but looks heavy:
This is on my plumber's 2000 Ford F-350 4WD 7.3 diesel.
I don't even know if they're still in business: