Underneath that drop in under the rail liner is a stock floor with an additional 11 gage steel plate over top covering the floor, part of the sides, and the whole front wall. Rear corners are also reinforced with 3/16" thick 1-1/2 angle tied into a 1/4" X 4" steel strip that runs across the rear under the bed lip keeping them square. I did that in 1987 when I first got the truck while they were still tight, they are solid.