non powered 8000 btu heater with through the wall exhaust

If I didn't already have a vented non-electric heater, I'd be all over that.

Those sq. ft. estimations for heating are about standard residential heating requirements. My 22' trailer has about 140 sq. ft. of floor but a lot of that is taken up by fixtures, of course. The 20K btu heater I use is operated on "low" or "pilot" most of the time. I think that 8K btu unit would heat a standard trailer or class C pretty well.