My 99 F250 Super Duty has slots molded in the side of the bed and wheel wells that fit fit a 2x6 perfectly. I cut three of them to fit and used 3/4 plywood as decking. I picked up a used topper for $200 and installed it. Originally I used a queen mattress and it fit perfect. My ex and I explored all over in Alaska on a 2 week vacation. There is plenty of room under the bunk to store a small camp kitchen and assorted tools.
