You see that rectangular thing with the vent grill mounted on the right side by the helmet near the ceiling.
That is a RV furnace, Suburban SF-30-F 30,0000 btu.
Cost to install:
Suburban SF-30 on Ebay or equivalent - under $400
Propane tank - $40
12 volt Battery - $50
Hose, wiring and thermostat - $100
This furnace will heat the inside so hot you can't stand it, if you wanted.
The attached pic of the outside vents is how the vents are on a SF-30-F model. A SF-30 without the last F is the same furnace but it has the big rectangular cover on the outside with the vents integrated. The F model is a cleaner installation as long as you have access on the inside. The non F model is for when you won't have any access from the inside, like how they are installed inside a motorhome behind a cabinet, etc.