Well, we finally got our new baby (2004 Kountry Star 3905) home on New Years Eve, and started the furnace on January 2. It turned cold here that night and for the next 3 days, the warmest was -26C (-14F) andit went down to -40(C or F,its the same) or more at night, (that does not include the wind chill; with that the temps were -50 and below) and the furnace kept the interior warm (20C or 68F), and the basement at just around freezing. It didn't run all the time, either. And that's without skirting, and nothing in the basement, and it was at -15C (+5F)when we started the furnace! We don't have water in it yet, we were just doing a test. We still have propane in the tank -not much- and turned it down to +10C inside (about 50) inside after the 3 days test as we aren't living in it, for the last couple of days. That 32 gal propane tank is great! It's supposed to warm up some tomorrow with a high of -5C (23F) so we can go brush off the snow and bring in the slides, so we can fill up the propane. We wanted to rent a big tank, but we will have to make it stationary and fully skirted and insulated if we want to try to convince them to hook one up here. We are running the coach on the 4 batteries and a 15 amp cord now, and the batteries are doing fine, but we are only using lights and the furnace. The fridge was on for a day, on propane, and it works fine too!
We calculated the fuel mileage our friend got with it when he drove it up, and he got 9.2 mpg US, traveling at 70 mph for the whole 350 miles. We expect to get even better when we are traveling at 55!
So we are doing the happy dance that this was definitely the right choice for us!