Fred, the way you heat sucks.
Torpedos, any non-vented propane heater, throw a ton of water into the air. And I'm not working in propane fumes all day, fuch dat ship.
I'd look at insulating your work area(s), frame it up, use steel stud/steel clad if worried about fire. Get some insulation and
VB in there and a properly vented heater.
Maybe you can foam existing walls?
You need a customer/buddy who's in HVAC
30X50' steel clad (in/outside) pole barn, 12' R20 walls, R40+ ceiling, 2" insulated overhead door heated with IIRC a large 120k direct vent gas (propane) furnace. I mounted it on it's side near the ceiling.
Emergency backup heat I could re-install the wood stove the insurance company made me take out about 10 years ago.
Con for my direct vent gas (propane) furnace is it can't freeze (water trap), so the heat always has to be on. I work from my shop so no big deal for me. It's a tad loud, expected as it's open to the shop area.
Pro is I can legally paint, insurance and code good, etc., as a direct vent has no open flame. Furnace will keep up with a small parts paint booth.
This spring I'm installing AC, too hot and humid in the summer.