I have never needed to make charcoal, but you got me thinking (something I don't seem to do much of these days). I wonder, assuming that one has access to empty metal drums, if you could take a 30 gal drum, cut one end out, punch holes all around the sides (the pointed end of a pick works well for that), then fill it with some paper and your wood, and lite it off (like the burn barrels we used to be able to use in some parts of the country). Once is it burning well, take a 55 gal drum that has one end removed and turn it upside down over the smaller drum, in effect sealing the fire inside. When the oxygen inside of the drums has been consumed the combustion should stop. Kind of like a char cloth tin. I suspect that timing the snuffing part would be critical...