Personally, with the ragged poptop I have, I don't worry too too much about
the combustion gases from my Mr Heater Buddy. It's like having a built in
chimney, at a fraction of the cost!

Radiant floor heating might be an interesting solution to the problem. Nexus
of tubing under the carpet, tiny pump, tiny on-demand propane water heater
mounted someplace outside...anyone tried that?