Your fine. In fact you may be more then fine. You didn't say how cold it is going to be?
I can go camping for a weekend in 40 degree weather with 2-6 volt golf cart batteries and still have plenty of power left over. I do have LED bulbs though and I keep the furnace at 55-60. The furnace fan draws a lot of power!
As for the propane I only go through about 2 tanks a season. I don't use the furnace often though. You get a lot of BTU's from one tank of propane. That's why it's used as a fuel.
The fridge uses very little propane. Especially when it's cold outside. It does draw a little power but, not a awful lot. The furnace fan will run your battery down a lot, lot, lot, quicker then the circuit board on the fridge.