Unfortunately we only have baseboard electric heaters in the home...no gas. We don't have gas service available on our street either. Our neighbors seem to either have propane heat or oil heat. I suppose the electric is always an option. I have had experience with the oil-filled electric heaters, but due to the size of the area they don't do much. It takes 2-3 hours to make a slightly noticable difference with 2 of them running, plus if you run them on high they pop the circuit breaker because of the current they draw. I suppose I'd just have to shop around for the right heater to do the job.
Also, as far as size, the basement is as large as the whole house, which is a 3 bedroom rancher, so it's pretty long. Volume wise, it is about 2.5 times the size of our 2 car garage..so it's big.
http://www.heatershop.com/indoor_gas_space_heaters.html
I did just find these, which there are a couple propane options. I'm wondering if anyone has any experience with something like this