I've seen it done before (aquarium in a garage) here in Toronto, where the tempature dips below freezing in the winters, and the summer high's like to hit over 100°F during peak months. This was in a non-air conditioned garage, and only heated on demand... (when he was working on a car, then he could turn on a heater in there to warm things up.), but it wasn't a constant temp... HOWEVER, was he kept the place very well insulated. This was in his garage where he built cars as a hobby. He said he's never had any problems, except there is now a crack in the side of one of the glasses where something hit it carelessly, and he had to silicone it up.
This was a few years ago, while I was still a freshie, so I never really asked (or would've understood) the precautions he took... his tank looked to be around 180g, which I assume could play a role as well... (larger bodies of water take longer for temperature fluctuations to occur.)
I think if you took the precautions for nothing to accidentally fall into the water, and if you were to be starting engines all the time, then possibly port a hole through the wall, make a custom little box to house your air pumps, and have it draw it's air from outside instead of within the garage, and of course have the appropriate chillers / heaters, then you'll be fine.
It'll just take a little extra planning is all...