Simply opening the door isn't enough to replace the air inside, so it is remaining hot, moist and stagnant - perfect for mold. You NEED some kind of exhaust fan in there to pull air out and take it somewhere else. My squirrel cage fan came with a regular grounded plug that plugs into a normal outlet, so no hard wiring is required. You may, however, need to cut a hole for the air to exhaust, but that is pretty easy, IMO. Case in point, you need to be constantly moving air out of the room or you will have moldy buds.