It's spring so this is not an issue I have to worry about for awhile, but I'm still looking into it. I'm in a shed shop which I plan on being temporary as in a few years, so I don't want to put any insulation or elaborate heating systems in. In my climate rusting from air moisture isn't a huge issue. My shed is about 8'x20', a bit small but works. This past winter before I had wood working equipment, I would use a 15,000 BTU tank top propane heater when I would work on my motorcycle. It wasn't bad, I measured when the outside air temperature was 15 degrees, and after a few hours it brought the shed up to 35 degrees measuring in the non direct heat. The primary issue I've heard about propane is that it adds way more moisture to the air than the humidity ever brings; I've heard guys say they put on their propane heater for a few hours and it left a coat of rust on their machines... I also think electric would be inefficient. Maybe I would be better off bundling up and using no heat, and bring my materials inside the house for finish. I plan on using my shop heavily in the winter time because most my hobbies revolve on outside stuff and gardening; I typically do absolutely nothing in the winter.