Kid TT-01, the problem with the 12v fans is they do not run all that well when plugged into the receiver. They really need 12v to work well and spin fast enough to provide enough cooling to be effective. The only way to get them to work a little better is to solder the wires from the fan, straight to the battery when you solder the ESC wires on, but if you dont solder your packs in, thats out of the question.
If you want to Run a fan or two, get the Novak fans or the Much more fans, they are 5v rated and they spin a lot faster and are a lot more effective. You Dont have to use the Novak or MuchMore fans, but its hard to find 5-6v fans of that size in the electronic stores.
Hope this helps.
Mugen MTX & MRX
"He who dies with the most toys wins" - Phil Harris