For me 50 is a perfect temp to be working in the garage, I would never make it any warmer and when not working I'd run it at 35 or 40.

For now I'm suck with a propane heater that I just run as needed. I have a 100,000 BTU natural gas furnace that I could hang in there but I plan on moving in the next year or so. I'll save it for the next garage!