tom,
Try it first without a fan. Fill it up, as much stuff that you can pack in there, shut the door and keep the temp under 100. As long as you have some venting at the top you should get good results. Stuff starts cracking with a fan. I have two dishwasher kilns and they are self venting so i didn't have to do anything else. The trick for mine is to not open the door for at least three weeks. The other trick is to do as many pieces as possible. The humidity builds up and controls the heat somewhat and gradually dissipates as long as you don't open the door. The bottom of mine are not sealed tight where the motor was removed, just a reflector setting in the hole. I'm sure this allows some air to flow from the bottom and up thru the vents. They work good.