Finding an adhesive that will bond to fiberglass and nylon, delrin, uhmw could be tough. If you are not too attached to the carpet liner, you could remove all or part of it and glass in a metal base to hold the screws. Simple rectangluar tubing would not have to be more than 1/2 x 1 inch thick and you could cut two long pieces or four short.

Otherwise a truck vault $$$$$ or a simple false bottom in the bed would allow invisible rod storage.