Whatever you do, just make sure to cut away the old rusted sections and seal up any overlaps between the old and new pans. Personally, i cut out my old pans and rebuilt/beefed-up the floor support area. I then created a small metal "skeleton" and laid several layers of fiberglass. I know fiberglass is not the preferred method but I work a lot on marine applications and know how to build up the layers and get it to stick right. Been 4 years now with zero issues. Once the repair was complete I used bullet liner (bedliner) to completely seal the area and keep it dry. It won't last forever but should be in there a good while.