This is awesome. The big issue for me when I've considered this is the operating conditions. You're hosting a linux board near a 250 degree source of heat that may be operating in ambient conditions that range from 35F and very rainy to 100F summer smoke.
The board doesn't have to be near the fire. Even the fan is separated. I 3d printed a fan mount that threads onto a pipe that runs into the firebox. The board' temperature range is 0-70C, so freezing temperatures would be a problem, but high temperatures. The rain would be an issue though.
