I dont know from direct experience but while I was in college I had a friend named Quoc that lived in Houston, I bought alot of my sps from him, and he had a huge inwall tank (with the display and frag tank in the garage). I know his main problem was temperature control. Here is a link to one of his reefkeeping magazine articles, he talks Alot about the pros/cons of his garage setup and the issues involved. (Beware: AMAZING TANK)
http://reefkeeping.com/issues/2007-08/totm/index.php