Hmmm... I built something like that ;-) Mine consisted of a plywood box as well, but measured 4' x 8' x 4' for a total of 128 cubic ft of drying area. Instead of a light bulb I used a residential 40 gallon gas fired water heater. A ciruclating pump (and expansion tank) moved the heated water through radiant fin tubing where a couple of fans moved the heat up into the box. The box was lined with a food grade surface and insulated. Worked only 'okay' as the water heater couldn't quite get hot enought for me. Just finished dismantling it this week. Gonna build a bigger, better one soon :-) -Jim C Mild to Wild