the exact same thing I have. That part is crucial for a rubbermaid grow. If you're gonna keep it closed all the time, excepft for when you're in there doing shit with them, it's going to get HOT. Like a buck 25 hot with 8 lights glowing in there. So the exhaust fan absolutely has to be a good quality. I bought those 2 desk fans and they did shit. I put this baby in and my temps are in the 80's always. In total it cost me $30 bucks for the booster fan, $6 for the flange to connect it to my box, $8 for a medium duty tool replacement cord, $1.50 for some splicer screw caps and $1 for electrical tape.
Fan:
http://www.homedepot.com/webapp/wcs...-_-100067594&ci_src=14110944&ci_sku=100067594
Cord:
http://www.homedepot.com/webapp/wcs...D27X-_-100661442&locStoreNum=4173&marketID=68
I cant find a picture of the flange but if you go to home depot to buy this stuff it's in the aisle with the fan. It's a small piece of ducting with a flat flange on one end to connect it to something. It also has adhesive foam on the bottom so it'd perfect for a grow box situation.
If you do this fan set up man you will be a happy dude I promise you that!