I have both my helmets running off 2 9v batteries in parallel with a switch and forward indicator light to let me know when the cells are low. Parallel is IMHO the best way to wire the things up since it takes the combined 18V and halves it instead of running 9 separate volts to each fan. They last a bit longer that way on premium batts. I can turn them on at 8am and there running at 8pm.
Also, use heat shrink tubing...it's your friend. Especially when you have 72 volts in your bucket. =)
Novall, I'd love to see your fan set up as I'm at the stage where I'd like to fianlly install my two 12V fans. I'm pretty good with simple circuits, but I'd like to be certain how to wire everything before i start and mess up some thing.