I installed aluminum diamond plate in my bed about 10 years ago. I use my truck all the time as well, and didn't want to invest in an expensive wood kit just to watch it get beat up.
I used 3/4" marine plywood as a subfloor, coated with fiberglass resin on both sides (no stain or cloth, just the resin) for waterproofing. I believe the bed is 50" wide under the corner strips, so I split two pieces of plywood lengthwise 25" wide by the length of the bed, and then tucked the edges up under the corner strips. I then layed 48 inch wide aluminum on top of the plywood, centered between the corner strips. I just bolted it all together and that was it. Nothing fancy but very durable. I would have preferred a 50 inch wide piece of aluminum so I could have installed it under the corner strips, but nobody local had anything in that size.
The attached pictures aren't very good but they're all I have:
