Is the fan on only when spraying? It seems like a fan would just draw dust in if left on. Shouldn't they have doors to keep dust out after spraying is done? (I'm guessing yes, but $$$ prevents most from being cabinets).
I'm curious because I saw a cool article on building one with a squirrel-cage fan from a furnace. I can get those free at work (used, of course) and I have a ton of scrap lumber/plywood.