Bay Area Dave asks:
Sorry. I was tired. Slot the insides of all four sides with a router with slot cutter and a bottom bearing. Then use a chisel or shoulder plane to lift the "slot" piece off one side, forming a rabbet. Square up those two corners with the chisel. Round off the bottom corners at the other side to fit the grooves. Slip the bottom in place and fasten with either two dabs of glue--good use for poly glue here--two small screws into the rabbet, or some kind of "you work it out" strip of wood fixed in the rabbet to hold that side in place. Twere it me, I'd make the rabbeted side the back.
You'd have your basic slots on three sides, a rabbet on one side, and shouldn't even lose much load capacity, while retaining a fairly decent "I meant to do it that way" look.
Experiment on scrap, of course.
Charlie Self
If you want to know what God thinks of money, just look at the people he gave it to. Dorothy Parker