I built my first one from OSB...stood vertical...chicken wire bottom with a ceramic base for the light mounted in bottom and lined with heavy tin foil to reflect the heat up.
Put a vent near top on one side I could open or close to help regulate heat and let the moisture out. Drilled hole just big enough for meat thermometer in front of door. Also made one big enough for the OUTSIDE probe of a humidity gauge with it mounted on outside. Put a single 100w bulb in bottom and in that narrow 2x2x8 foot closet it would get warm enough to keep my hickory at around 10% relative humidity based on the temps and high humidity outside all summer long here in Charleston.
I am about to build a new one that lays down as I had to flip the stave on opposite ends to make sure one end did not dry out too much but having on a dimmer switch helps regulate it all nicely. This time using some leftover OSB again I have in garage...lining with insulated foil...3 bulbs on ceramic mounts...maybe 60-75wattes....piano hinge on lid but going to make it a box first and then cut top off for a lid. I am ready to finish my hickory bow I started couple weeks before 9-11 and never finished as I was deployed for almost the next two years. Then I retired...started new job and just not had desire to finish it. Now I do so time to finish.
It is roughed out and ready to start floor tillering so need the box before I start. Thanks for the thread to get me motivated again.