nviaircrew, The damage on my truck was only good roads, although a little rough coming up North on Hwy 101 from California into Oregon this spring.
I don't think the 5th wheel prep package adds any stiffness to the bed, but mine still had the hard plastic pucks installed under the rubber mat. I still think that contributed to the damage on my truck in the first place. But after seeing your damage I may be mistaken unless you still have the pucks installed also.
I also have the Torkift frame mounts and I am using the old style springload tie downs, maybe I am tying it down to tight?
I think I am going to built a set up like Camper_Jeff_&_Kelli has. I may drop the bottom of my camper and inspect the supports just to make sure nothing is broken. I don't know how the camper was treated before we bought it.
Tim