Many people think this is a bad way. But we got a HPX from cross implement and we didn't want a plastic liner nor a spray in. So they took 3/4 plywood laid it down and sides flush to the top rail, then put angle iron across the top to protect the sides. Then sheet metal on the tailgate. It's all secured by counter sunk bolts. it won't rot since it's treated. Painted black and then sealed with silicone in the corners. Stuff don't slide and when you throw stuff in the bed the wood absorbs the blow. Its very cool I think, never had to replace yet after 4 years. It kinda hard to explain but I'll post pics when I get home