Frame strenghtening:

Well you've got all kinds of components that have to work together. Tires, axles, suspension and frame. I don't know if you can simply just swap out 40k rears and suspension with 46k rears and suspension and throw a pair of insert rails in and roll with it or if the manufacturer would have to re-rate the truck.

 

Increasing the frame strengh can be done with new rails, inserts or double frame.
Aluminum frames can be strenghted by removing the aluminum and install new steel rails. I have seen steel inserts in an aluminum rail but its just asking for long term corrosion issues.
At the end of the day, it doesnt matter what your truck has, its what the sticker on the door says it can haul. To get someone to certify your truck for a higher gvwr would take quite a bit if anyone would even consider doing so. Sounds like you just need a different heavier built truck for what you want to do with it.

 

i think on pick up trucks, you can "box in" the frame rails. that is, to add steel to the side of the rail that is open. if i can find some pics, i will post them. BRB

 

ok here, you can see the outside, AND inside of the frame. notice how you do not see inside the frame, as it is "boxed in"



in this pic, you can see inside the rails, as the inside is open. the front area is boxed in, the rear section is not

 

4000lb camper on a 3/4 ton......

Only proper advise is buy a differnt truck.. that is a recipe for a law suit if you get into an accident. This is not 1974 anymore. You need a F450 for that size camper.