Airport Extreme (n) Mounting on Ceiling/Wall

I'm looking to roll over several of the old "domed" Airports which are conveniently wall and ceiling mounted.

Apart from the issue of sourcing the actual mounting bracket, now a third party purchase, I've heard that there may be over-heat issues if the new base station is mounted on a ceiling upside down (the logical way appearance and broadcast wise), or if right way up, the top can't be flush with the ceiling due to the heat sink being uppermost.

Any comments or warnings?