i built this box for steam bending guitar sides. the steam box sits on a pan of boiling water on the stove and steam enters through the cutout in the bottom. i designed/built/used it this evening, it seems to work pretty well.
jack - i used it for about 20 minutes and barely made a dent in the water level. i bet it would steam for a couple of hours if you started with plenty of water in the pot.
Great idea, I would not be able to do that at my house though! No way I'd get to steam in the kitchen. My wife had a hissey fit when she discovered the red oak I had stored in the garage freezer for future chair making, the kitchen would be off limits!