I did not like the kerosene heaters I tried. They gave off a diseal smell. I am now using a propane heater. I have a bench that sits besid the heater so I can put the epoxy and paint to warm up. I have sprayed warmed paint when the air temps were in the 30's. If the parts are small, you can put them in a big card board box with a 100 watt light buld for heat. The box will warm up to around a 100 degrees.
When building in a real cold garage, the biggest problem I ran into was gluing my gloves to the plane.

Next is your feet will get cold. Gets some of those foam piece for a play room that interlock. It keeps your toes warm and off of the cold, cold concrete.
I to cover inside. When it gets cold the plastic covering gets stiff and hard to work with.
Dru.