I don't think it's crazy. I was thinking of using an aquarium heater in a couple gallons of water in a larger home made incubator as a heat source, humidity source, heat sink, to stabilize temps. Wait, just thought of a possible problem. you need air exchange, and generally the holes in the bottom let in new air and the old air goes out the top... hmmm... well, if you had tubes that would siphon cold air down to the bottom of the unit, and it would be warmed by the heater/heated water, whatever, then it would rise and go out the vented area at the top, whatever you made for that. Passive air exchange is the only problem I see with this so far. I like it and it makes my wheels turn in my head. Thanks. I have a sixty gallon show, which means tall and skinny, front to back, that would be GREAT as a HUGE, home made incubator, plus it has all the under gravel filters for it, which could be re-purposed for keeping the eggs and hatching chicks abive water level.