The best way imo would be to use a relay. Get a SPDT 30A relay and use the remote lead to switch the relay on and off. This prevents you from having to worry about having to turn on and off the fan. A direct fused line from the battery would go to the relay and then to the fan(s). The wiring diagram can be seen here http://www.the12volt.com/relays/page5.asp#rtol. It's relatively simple to hook up, just make sure you have a fuse 18 inches or less from the battery.
Igitur qui desiderat pacem, praeparet bellum -- Vegetius
"I told her about my conversation three years ago with the political leader of Islamic Jihad in Gaza. "What's the difference between suicide, which the Koran condemns, and martyrdom?" I asked. "Suicide," he replied, "is done out of despair. But remember: most of our martyrs today were very successful in their earthly lives." In short, there was a future to live for--and they detonated it anyway."