Since you seem to be primarily concerned with saving propane, you might want to look into getting a catalytic LP heater. We have one that we use when boondocking (a Mr. Heater Big Buddy) and it puts out a lot of heat on its high setting (18,000 BTU) yet it only sips propane compared to a typical RV furnace.
https://www.northerntool.com/shop/tools/product_200307957_200307957?cm_mmc=Google-pla&utm_source=Google_PLA&utm_medium=Heaters,%20Stoves%20%2B%20Fireplaces%20%3E%20Propane%20Heaters%20%3E%20Propane%20Portable%20Heaters&utm_campaign=Mr.%20Heater&utm_content=173635&gclid=EAIaIQobChMI9o6N5v2v2AIVCrjACh11igHtEAYYASABEgLeT_D_BwE
My parents full-timed in a large 5th wheel for years, often in very cold parts of the country, and their primary heat source was an Olympic catalytic LP heater. They can be used without power from the RV's batteries, so they're great for boondocking, and most of them can be run off those little disposable propane bottles. Some larger models are also designed to run off an RV's LP tank. That's how ours is set up.
They are indoor safe, but it's a good idea to leave vents or a window cracked. One down-side of catalytic LP heaters is that they emit a fair amount of moisture when operating, especially on max heat. In really cold weather, you can expect condensation to form on your windows, especially on high, but the cracked window and/or vents helps a lot.
Kev