Buddy heaters will turn themselves off if they become oxygen starved. In my motorhome, my Buddy Heater is my main source of heat when it gets cold. I feed mine from a 20 pound bottle via a rubber connecting hose. Crack a window and you will be fine. I also open my Fantastic vent fan just a bit to get the fresh air circulating, knowing that hot air rises.
If you are sleeping in a small place, such as a van, the natural tendency is to your place the Buddy Heater near the bed. As important as keeping a good flow of air, is also insuring your safety by providing space around the heater from compustable materials. This is particularly important regarding your bed covers. Roll over at night; your covers shift; slide off your bed right onto the heater. Watch out, Buddy Heaters get really hot. Be aware when you are using an open flame of any type; mount one or more fire extinguishers immediately available in your living spaces. Don't become a crispy critter because you are situationally unaware.
Just my opinion . . .