I have a sheet of 3/4 exterior plywood in my bed. It is heavy. No need for the 300 layered varnish or expensive marine stuff. I slip it in the back, slide it under one side of the strips, it will fall to the frame, and then slide it over under the other. I try to get it centered. And I don't worry that it is not 50 inches. Mine hasn't slid around (it is probably held in place by the carriage bolts which hold down the cross braces) so I don't bolt it down. That's cool, saves money on the strips and other nuts and bolts.
Simple, easy, and inexpensive. I use my 55 as a truck. What ever I want to through in the back goes there. And most of my truck is primer. Guess I look like a redneck. Maybe I will paint it next year.
Oh yeah. When this sheet gets worn out I will replace it with a fresh one at Home Depot. Maybe I will drive it in a parade.
