On my previous truck I had the rails in the bed for a reese fifth wheel hitch, then went to a TC, but kept the fifth wheel hitch. I made a 2x4 frame with the 2x flat bridging the rails, across the front and read of the bed so the 2x were spaced ~ 16" on center (over kill). The sides were notched to fit around the rails then covered the frame with 7/16 OSB. It raised the TC about 2" from the bed but I did not need to remove the rails and I got a flat bed back. The platform could be removed when wanting to use the fifth wheel hitch
Jim