When I lived in Canada in extreme cold temps it was common to warm up vehicle engines, thaw rv systems by tarping/ skirting them, then place a long (6-10') stovepipe on the ground ending under the unit, light up what us pipeliners called a Tiger Torch, a up to 300,000btu propane weed burner, flame set accordingly, placed at the open end of the stove pipe so that it drew in outside air exhausting under the machine. Thus no flame under the unit, just heated air, lots of it.
We even used cargo parachutes to cover entire heavy machinery , then used the heat this way to inflate it like a hot air balloon.
