Not to be on the negative side, but why would you want to keep your cigars in the garage? Especially when you know that it gets warm in the summer? I know ID can get warm in the summer.
A friend that smoke cigars infrequently (he actually got me started in smoking cigars some time ago) asked me the other day if leaving a cigar in his car would cause a cigar to not smoke properly and have the wrapper come apart. I was a little amused by that, inside car temps in FL in the summer are brutal.
Rebecca's use of ice packs may not be the most common method to keep humidor temps down, but if it works I say go with it!