I have a friend who just purchased a Lance Camper to be carried in his new Chevy 1 ton. The camper would not sit flat in the rear tail gate opening. He had the opening modified by removing the radius side panel and had a body shop fabricate some "L" shaped panels that were welded into place, then repainted. Alot of work to carry a camper, not well designed by GM. I think this was done by GM to make that portion of the bed side panel stronger. Next time buy a Ford, problem solved.
Jim, your number is locked in my old computer, we killed em' call me for the whole story.