With the temps you are talking about, your best bet is to dry camp. Tanks will freeze unless you have tank heaters, and even that isn't a solid bet. We used to do it with our popup, use the bath house, no water in the trailer tanks, maybe a cooler of drinking and cooking water.
Using the LP furnace you are going to go through a lot of LP. Easily 20# tank a day, if not more. I used electric heaters and an LP fired Buddy Heater to take some of the load off the main furnace.
Not saying it can't be done, just not easily or cheaply.
Aaron