On the 18 you can probably do 3 on the top rack if they're not too big and 2 on the bottom. On the 22 , you can easily do 4 average size on the top and 3 on the bottom. Anything more than that you might have some air circulation problems.
This gentleman also sent a message to our Association's website asking the same question. The festival he speaks of is real and I'm sure he is looking for some real help. We referred him to our events committee and he is talking to them.
Not everyone is a huckster and out looking to make a buck...
Don't need all of these immediately, but here's a pretty good list of things to keep an eye out for when shopping.
http://www.virtualweberbullet.com/accessories.html