I collected Biven's articles from Rifle magazine, photocopied them and assembled a binder of the articles in a book of my own. Among them, the article about the damp box was most useful.
I was at the dump one day, and someone had disposed of a bunch of 3/4" plywood cut off ends that worked out perfectly for my damp box. Without measuring, I'm guessing that the box is 12" square and long enough to suspend a 50" barrel above the water bowl. In the bottom of the box is a compartment lined with asbestos (I know, I know) housing a ceramic fixture that holds a 300 watt bulb for heating the water. There is a second fixture and bulb about mid way up the box to heat the compartment. A dimmer switch on the outside of the box controls both the water temp and the temp inside the box. Cup hooks in the ceiling support barrels via their wooden end plugs and screw eyes.
I added trays at two levels for smaller parts, ie: butt plates, etc. and there is space behind them for the barrels. I rotate the barrels every three hours, muzzle to breech, and get a very even fine grained brown using a Neider's recipe for the solution.
I never leave power on when I['m not in the shop, and definitely overnight. But I sometimes leave a set of parts overnight in the box, to continue browning the next day. If anything, the rust is more even this way. I find that five or six applications of solution every three hours gives me a deep fine rust that I sometimes only burnish with a roll of canvas cloth, and sometimes I card the rust off between coats for a polished brown. Boiling a browned barrel in distilled water for twenty minutes gives me a blue/black finish that when carded hard is truly beautiful. Here's a few pics...