Well something new

Seems like it could work. The only issue I would have is storing a huge, heavy, awkward 6.5' x 5'(wide) x 2'(high) metal bracket. I guess you could somehow rig it up to sit under the camper when stored but that just seems like a lot of extra effort. That is a deal killer for me. I just have enough room for my camper in my rv pad in my back yard, I don't need something else with almost the same footprint as my camper. Also, it looks like you'd need to build a 1" support or pad for the spaces in between the metal brackets running out to the edges of the bed. I wouldn't want my camper just sitting on the bracketry yet unsupported in the areas near the wheel wells. Not complicated to do but requires some work and effort to do.

I do agree that the ball can support 20-30k of gooseneck trailer but that force is directed right above the ball and the leverage on the plates is smaller. Force is not but the leverage of that weight is significantly smaller. You are now extending quite a leverage force out beyond the beds of the truck bed. There are 4 bolts holding it down but I bet that system extends another 2.5' out to the sides, let alone the fore and aft lengths. As another poster mentioned, on road - maybe, offroad - no way Jose.