I here ya. My freezer is in my unfinished, walkout basement.
Obviously, a 2 stage controller makes things a ton easier.
Until you get on, you have to monitor the fermenter and adjust accordingly. When warming in the freezer, I generally set the temp around 60 during active fermentation. The heat from the yeast raise it another 5 degrees or so. Once the yeast start to slow down, I'll set the temp up to 65. That is really going to depend on the temp in your garage though.
You also might need to manually switch from heating to cooling during the day. eg if it is 65 during the day, the freezer will trap the heat from the yeast and easily raise them temp to 70+.