It was my first crack at aluminum welding -- so cut the welds some slack
1.5"x1.5"x.120" tubing with a scrap piece of a Frito Lay chip truck wall for the tray (52"x22"x.090"). I made the tray large enough to hold a bunch of rubbermaid action packers and/or 5 gallon gas cans and/or water jugs. Or anything else you can toss up there and lash down.