DIY Slide In Camper questions

Background - I currently have a homemade 8 foot truck camper with a slant front that I built for a dodge dakota. It's just under 80" wide. The end of the camper sits on the tailgate. I had originally make it 6.5' long to fit with the tailgate up but it was too small so I rebuilt it longer(and fixed a lot of other mistakes in the trial build). The camper is currently on my 2500 Sierra(lifted up with 2x6s and plywood since the sides are about 3" taller on this truck) and I can close the tailgate. I use mid-grade straps to mount it inside the bed at the front and using eyebolts on the camper under the wings along the inside walls and then strapped to the frame under the back of the Sierra. Took it cross country and had with no isues.

The camper is configured with a twin bed across the front under the slant, a counter on the pass side with a 3 way fridge under it at the rear and a seat on the driver's side with a 5000 BTU house A/C again at the rear. It's framed with 2x3's and sheeted outside with 1/8" plywood. I did the poor man's fiberglass on the exterior and have had no leaks. It's not pretty but it works.

First question - I've read here and on several sites that a slide in camper should not sit on anything other than the truck bed. I am kinda confused as to why this should be so. I have a 14ft ladder rack on my 8 foot bed truck that probably weighs 250lbs. I have probably put over 1000 lbs of lumber on it with no problems.

It would seem to me that having the camper sit on both the bed and the side rails would give it more stability. If it is more than an 1" higher than the sides, then the camper could wobble side to side under crosswinds, which would not be desirable at all. Plus, if using exterior tie downs, won't that pull the wings down onto the rails to an extent? I also can't imagine the weight sitting on the rails will hurt anything.

Second question - Supporting a cab-over. I'm thinking about building a larger camper now that I have the bigger Sierra. I'm debating doing a complete floor over rail since it's not really that much tall overall(I'm only 5'8" and my current camper interior is about 6' inside). That would only really add 20" in overall height and still be lower than a 5th wheel in height.

I'm just trying to figure out the best way to do the cab-over. I didn't do on with the current camper because of the drag on the dakota(it's a V6 Mag-none and pulling a flat front trailer kills it - the slant front doesnt). I don't really know if I need the whole width of the camper for the cab-over(probably going to do 8.5' wide this time).

What's the best way to support the weight of the cabover with 2 adults in the bed? I was debating running 2 2x4's stood up down both sides of the whole camper but that would only support the sides..... Could I using cables at 3 or 4 places at the bottom front of the cabover going up and then back to the back ot the camper work? The cab-over would probably only be about 4ft out with the rest inside the main part with storage under.

Thanx