This rack box is made of russian birch ($48/ 4x8 sheet), and although I have only built one so far, it appears I can get at least 4 out of a sheet, with some left over. The front and back have a 1/4" X 1/4" lip that is dadoed into a second layer of 1/2" ply around the front and back edges that is 2&3/4" wide. This helps align and hold the lids in place as they are clasped and gives extra structural strength to the box and gives 1" of wood for the rack rail bolts to go through.
Almost finished, waiting on the rest of the hardware:


