Here is my bed rebuilt using stainless strips, stainless bolts and 3/4" treated plywood. It takes a bit more than 1- 4 x 8 sheet. You can get the cut lengths here (
http://www.gmcpauls.com/47-72_BedWood_Info.htm).
The truck works as a yard truck so the treated lumber is the best choice for me. The stainless can be reused & buffed up when I rebuild for show (yeah right).
Blue666
Robesonia, PA
(Currently working in Afghanistan)