Khalid and CarveOne- thanks for the feedback re the 12v input and putting a 7805 regulator on board. I'll keep it under consideration for the next PCB revision.

Khalid- I posted something in the SuperPID thread about small fans since I did some testing recently. If your little 12v fans still run ok on 5v, even if a bit slow, they will still move some air. Your enclosure is maybe 0.1 cubic feet and even a slow fan will move 1 or 2 cubic feet per minute so it can still provide some serious cooling. A good 50mm fan will move 6 or 7 CFM.

The 40 and 50mm fans generally draw less than 200mA from 5v (only a small amount), so that should be fine from your regulated 5v supply.

Good luck with the trial run!