Used to have my workshop in an old 16' or so camper trailer(just removed all thecabinets and walls. wasn't well insulated either). Didn't have anyplace for an indoor shop for a very long time. Been through a lot of very cold Michigan winters with that setup. Your fuel choices will determine what you use for heat. Natural gas from your house supply would be the cheapest I think, but I've never had that as an option. Have always used kerosene or propane, found kero to be the cheapest. 1gal of kero will run my 10-12000 btu heater for 12 to 14 hrs. Had a catalytic propane heater, 8000 btu, that would only run 8 hrs on a 20lb cylinder. After going through a few cylinders, i quit using the propane heater. The kerosene heater could bring that trailer up from single digit temps to sweatshirt comfort in about 1.5-2hrs, and i would have to open the roof vent after about 3 hrs. Main drawbacks to kerosene are the smell and the fact that the heaters are not output adjustable. They are either on or off. Thankfully my shop is in the basement now, with a 1500 watt electric as supplemental heat. I think electric might be even cheaper than nat. gas. seems to be here.