I did all of the work on my
'69 Mach 1 in a 10x20 storage unit. Among the many difficulties was never being able to get anything done in the cold Western PA winter months.
I decided to try a dual head radiant heater that mounts on a propane tank, similar to the one in
@DonChristie 's post, to see if I could get the garage up to a temp that I could function in. I placed it so the garage door came down to just above the heating elements, with most of the unit physically outside radiating inward. The door was open probably 30-36" and there were two openings in the upper walls for roll door access. I figured I'd be okay.
It wasn't long before I suddenly realized that I was falling asleep under the car. That gave me the shot of adrenaline I needed to get up and out of the garage. I stood in the cold taking long, slow deep breaths until I felt my awareness slowly returning. That was way too close a call. Hank Hill be damned, I'll never go near another propane heater again!
I now have an actual garage with a mobile home furnace burning home heating oil. The garage is 30x40 with a 12' ceiling. That little unit kept the temps at 50-55 all day every day, all winter long, and only used a shade more than half of a 275 gal tank of fuel. That's about $160-200 for the season. I'm pretty happy with that.