Furnaces, Water Heaters, and Air Conditioners all fall into a category of you best do it right from the beginning. Or you will spend more in the long run.
I believe there is a reason commercial RV builders select certain major component. No….. not because they are trying to go cheap. Quite the contrary.
I believe the driving factor has to do with liability issues relating to safety. Secondly, avoiding service issues or component failures during warranty periods.
For the above reasons, and especially my safety or the safety of my loved ones I believe the RV type forced air LP furnace it the safest means to heat a small confined space.
First, there is a combustion chamber that intakes outside air, and exhausts to the outdoors. Via a sealed heat exchanger, in living space air is safely heated.
Unlike radiant heaters, there is no open flame or hot surface that can come into contact with things like bedding, paper products, or clothing that might make contact in the night. Often very real scenarios with kids, pets, or simply rolling over in bed at night.
Think long and hard before you subject yourself, loved ones, or pets, to numerous hazards using other types of heating methods.