You can use a small 5V fan, putting 7.2V into the fan is too much voltage for it. GO to Radio Shack and get a 5V voltage regulator (1.79), take the voltage from the receiver into the voltage regulator and into the fan.
I put this setup on my ESC in my Stampede to keep it cool because its enclosed in a box to keep the snow and water out. TO check it out I had an MIP temp gage bonded to the heat sink. The fan took the ESC from cooking hot to just slightly warmer than air temperature.