Chris,

        I would not use a propane heater (unless externally vented) in a camper
when sleeping (or tent anytime).  A few years ago, 4 or 5 people died in
Massachusetts, not far from where I live, doing just that in a tent.  I
know you opened the windows a little, etc.

This is just too dangerous - as the saying goes "carbon monoxide is the
silent killer" You will NOT smell carbon monoxide.  Please just get a
warm sleeping bag - don't risk it - please.

John R
(who has slept out in -15 F deg)