Through a combination of gifts, purchases, and gift purchases, I have acquired 64 of the 100g tama from Braiders Hand. Right now, they are all in use, but eventually, I may have to put them in something for storage. Since boxes are easier to make than tama, I retreated to the garage to make these storage trays.
They are made from 1/2-inch thick pine boards, and each can hold 32 tama. My general rule for storage options is that you should always plan for twice as many whatevers as you have now. The corners are mitered, and the bottom is rabbeted and then set into a dado that goes all the way around. This lets the bottom expand and contract with humidity changes while still being 1/2-inch thick. There are no fasteners in the tray, just glue. I can make two trays from a single 6-foot 1-by-10.
It takes a while, though. Plus, it takes a planer (to turn 3/4-inch 1-by into 1/2-inch lumber), a table saw (to cut all the pieces and joinery), and a sander (so that everything looks nice and smooth). These trays might someday become become drawers in a kind of kotansu, but that day is probably far off.
Update: I realize that I did not do a very good job of describing how the bottoms of the trays are joined to the walls. I made a diagram –