I do not engage in illegal activities, but if I did I would cut a 4inch by 10 inch hole below my grow box and add this item for cool intake, also leaves a nice clean vent when your box moves
http://m.homedepot.ca/product/ProductDetails.aspx?productid=979007&lang=EN
http://m.homedepot.ca/product/ProductDetails.aspx?productid=979007&lang=EN