what are the outdoor temps going to be like-below freezing? does you non heated garage go below freezing (if insulated probably not but depending on how low the temps get it's not unheard of where we live). the issue you can get with a freezer absent power is the temp starts RISING and then it can get warmer inside of it then it is in the room it's sitting in or outside. what some folks in our neck of the woods will do (if you don't have wild critters that will get into it) is put frozen foods in open coolers (or bags) on their porches or decks b/c the outside temp will maintain those foods in a frozen status even during 'warmer'

periods of the day. as an example-we are not in your uber fridged situation right now but it's still cold so right now (noonish our time) outside it's 23 degrees while my non heated but insulated garage is sitting at 45 degrees. it can buy you days and (depending on the outdoor temps) up to a week or more of time.