We are using a Webasto Airtop st3500, its a diesel or kerosene forced air heater, very efficient, doesn’t suck down power like RV furnaces do, and quite compact.
Webasto Airtop 2000 ST. Runs Off Fuel Tank (1 Gal. Gas Per 24/Hour Run Time). 1 Vent Located By 3 Drawer Cabinet. LED Thermostat Control w/ Timer Fan Modes—Ventilation Without Heat.
Webasto Airtop 2000 ST
Warms cabin very fast; van can be off while running; quiet; uses very little fuelVery expensive; doesn't like to fire on unless van is under 60 degrees in cabin; maintenance is complicated and few can service gas model