I've used my trucks for a lot of hauling and the camper guides have never got in the way. If your material will clear the fender wells, it will probably clear the camper guides. I used to drill a couple of 3/8" holes in the guides, down low, so that I could put a shackle in it and use them for a tie down.
I don't think you need anything more rigid than you currently have, but you do need to transfer that corner load down to the bottom of the bed. That is what the two 8' pieces of wood in the valleys would be for. The foam is to make sure there is some "give" between the camper and the bed.
Good luck with your rig.