I just scabbed mine together out of 2x2's for the posts and 2x4's for the rails. I left the 2x2's long, and stuck them in the pockets. I then measured from the top of the rail to where I wanted it, and screwed 2x4's to the 2x2's with deck screws, level all the way around. Then I trimmed off the top of the 2x2's at a slight angle so they shed water. I never bothered to paint the boards, my truck bed is functional but not pretty.
