Since I do my high-speed runs in a confined area--and do a great deal of braking--heat has been my top nemesis. In an attempt to alleviate this, I'm testing a HUGE fan. Since I have two bodies--one beat-up one and one brand new one--I have a vent in the body where the rear window is to allow some ventilation.
I have tried two different fans thus far, and neither seemed to help. Got the fan at Radio Shack for $15--it runs on a mere 6 volts, so I have the power coming from the receiver.