Mine is sheetrocked and insulated. The apartment overhead is heated, I've never seen it drop below 52 in the garage underneath, with outside temps in the teens. In the 50's, moving around working and it feels fine. If i'm just standing around I have a small jet propane heater--haven't used all of a tank in 10 years.
Harder part around here is cooling in the summer, I've got a 2400BTU 220V window AC that I cut a whole in the wall for. It works pretty good.
