Campers have ventilation naturally.
I parted old camper and when I did notice earlier that electric cable box was venting the air under bathroom sink, it took parting out to notice big floor holes around the drainage pipes, who were never sealed.
I installed Chinese diesel heater in my latest conversion. They are very energy saving and quiet.
When propane heater makes coming on and off rocket, diesel heater adjust the speed depends on heat demand, idling slowly when heat is on low demand.
Have seen motorhome owners installing it with small tank that comes with it. When some smell can be an issue, you are avoiding low temperature issues and can fill it with 50-50 mix of kerosene/diesel.