I mounted a CPU cooling fan to my paintball mask because without it, the humid air would fog it up. Worked great and kept me cool until I got shot point blank in the face, and the blades flew off and cut my lip. It was an extremely minor injury, and I just attached another one since it worked so well.
I'd probably prefer helmet mounted cooling fans since that's more efficient than directing to the whole body, though that might be tricky and the extra weight uncomfortable.
How about a neck fan?
