The answer is yes. It is possible to have your mattress in the garage for long periods without damaging it. While doing so, there are a few factors that you have to keep in mind. For one, it should be clean and dry, and you should also have it in a sealable mattress bag. Also, look into the conditions of the garage and whether you can regulate them as the seasons change. The positioning of the mattress should be flat as having it on its side could warp it.