Mark, I don't know if you're stuck on electric heat, but I use something similar to this in my garage to heat my legs and it gets a bit colder here than where you are.
https://www.amazon.com/Dyna-Glo-RMC-...erosene+heater
I use mine in an enclosed 3 car garage and have never experienced any carbon monoxide problems, so if you're using it with the door up, you should be fine.