Coming in late to the game, but I went through a similar deal building a small cabin.
The blue flame type heaters have a "safety feature" that only works when the place is depleted of oxygen because the flame on the thermocouple safety valve starts to fade away in low oxygen (told to me by the HVAC guy installing a new heating system in my mothers house)
Also - the water products from combustion go into the cabin and everything is damp or walls rot.
Direct vent models are available through northern, menards, etc for about 2X the price, but what is your safety worth?
Using a direct vent RV model may make more sense if they are built to road vibration.
Ever look at wood pellet designs? Although I lean towards the convenience of propane.
