If possible get a 180cfm fan (inline or squirrel cage). Have a passive intake and let the fan pull cool air into the bottom and out the top. Also, if you use a rheostat you can adj the speed of the fan. As for temps, you'll have to run the lights during the coolest period as 84 degree temps are too high to cool your box. If stealth is not required you could use a plain old fan blowing into box.