Oddly enough I am working the same project! My design is very similar to yours. But I have to ask where are you going to get the fans for the unit? My structure has been completed and I am wondering where I can buy a fan. Thanks
any electronics supply place will cary the little biscuit fans. Radio Shack carry them in the harder to find 120v versions if you want a direct plug in version. most computer supply places will carry the 12v or even the 5v versions if you do not mind using an AC/DC adaptor.