DR-
I just bought my second P/U slide in camper last year. On both I have used a system (Happy Jack) that mounts to the front wall of the bed, and to the rear bumper. The camper attaches with turnbuckles. It works well. I have seen the systems that are mounted with a bar to the frame, but I don't like them. They reduce ground clearance, and you are always hitting your legs on them. I attached a pic to show you what I mean. The mounting bar is heavy steel, and runs the full width of the bed, and is attached with 8 heavy bolts. Two holes are drilled in the rear bumper, and the hooks for the rear mounts are bolted in. I have used both campers quite a bit off road, and they stay put. Key is to use a soft rubber matt on the floor of the truck bed before putting the camper on. Makes a big difference in preventing the camper from sliding around.
Larry