I use to keep several servers in the garage. I never had a problem with critters, and the temperature variations were pretty drastic (100F in the summer, 40F in the winter), but that bother anything. The biggest problem was dirt. Leaving only a few miles from the ocean provides us with a pretty humid and dirty environment. The fine salt and grime that would float into the garage would take out chassis fans in a year or two. I finally moved everything out of the garage, and spent quite of bit of time doing some detailed maintenance on those machines. The tenacity of that schmutz was amazing. It formed this thin film that required a hand scrubbing to remove. I ended up opening the power supply, carefully cleaning the inside and replacing the 80mm fan. So it is for that particular reason that I wouldn’t put servers in the garage again – unless, of course, I could control the air quality.