<I'm possibly being an old fuddy-duddy, but I wouldn't feel safe
sleeping with any propane-powered furnace running overnight unless it
was properly installed and vented (implying, a built-in furnace).  If
we're camping where overnight temps are lower than our level of
comfort, we only stay at campsites with shore-power so we can use our
electric heater.>

In addition to the dangers of using an unvented propane heater in a closed van, you are going to think you woke up in tropical rain forest. Talk about contributing to seam rust!       Jeff