I can't seem to find pictures of my carryall box, but I can describe how I did this. My box is slightly wider than twice its depth (front to back), so I hung hinged sidewalls that fold in against the front (vertical wall) if I ever want an open L-shaped platform. The sidewalls slope down a bit toward the back, to help maintain backwards visibility. The sidewalls are also equipped on their back (vertical) inside edges with short sections of channel iron to take up to three drop-in tailgate boards (2x8s). In addition, one of the tailgate boards can be slipped into shelves on the sidewalls to form a seat, in case you ever want to take helpers out to the woods or berry patch. Finally, on the front of the vertical (wood) wall I have mounted a couple of plastic tubes for tool handles and a wooden chainsaw scabbard.
BOB