Just back home from some off-grid camping, which is our preferred style. The old gravity furnace
keeps us perfectly comfortable in foul weather - and all the while untethered from civilization.
Come to think of it, we do most of our camping in the fall
, winter, and spring... after most everyone else has winterized and tarped their trailers.
Fan dependent heaters keep us from considering a newer trailer, but perhaps the maritime industry has something (a convective heat source) that may be retrofitted.