I used the Mr. Buddy heater in my RV2 with attached front and side panels on 2 occasions this last winter. I did not die from asphyxiation.
First event was 3 days in length and the temperatures were in the teens at night and single digits from the wind-chill. The second event hovered around freezing with brisk winds that brought the temperature lower and was plagued with a driving rain for about half of the 5 days there.
The unit is fueled by a bulk cylinder of propane of which I have a duplex splitter and run 2 lines - one to the heater and the other to the stove. I didn't feel the need to heat the tent while I was asleep. I used it to warm up the 2 spaces then hit the sack (both bags of the military issue sleeping system only) in comfort. The switch to turn it on was close enough to reach from my rack with self-inflating sleeping pad, so I'd turn it on when I got up - waited for the temp to rise, and carried out the plan for the day. My OZ-Tent is not air tight - there are enough gaps from joining the panels that there is always sufficient venting I didn't feel the need to heat the tent while I was asleep. The only condensation inside the 2 spaces was noted on the front paneled space on the peaked roof panels, but I could also attribute that to my respiratory exchange and not necessarily the evening and morning warm-up.
I assert it's important to have a space between you and the ground and/or a decent insulating pad with closed air cells... oh, there I go again with that whole air gap thing.
Much like my wife, a good piece of kit.