We're just coming out of our first winter fulltime in the Montana. We spent the whole winter in the northeast with many weeks well below freezing and saw temps as low as -2 degrees. The whole winter we only used two 30lb tanks of propane and the coldest it ever got inside was 64 degrees on the few nights it dropped below zero. Here's what we did...
Starting outside the hose is wrapped in heat tape then wrapped in pipe insulation. The frost free spigot it wrapped in some left over batted insulation then covered in a trash bag and we put a 5-gallon bucket over everything. (The spigot covering was a quick fix in the dark after it froze up one really cold night and we ended up just leaving it like that)
I rolled up a piece of insulated fabric in a plastic bag to fill in the hole for the hose and ran in an additional 12 gauge extension cord here. I also have an extra piece of the 2" rigid foam that I close in the convenience center with since the doors not very well insulated.
Next, I added 2" rigid foam insulation to as much of the underbelly of the 5th wheel I could including the basement areas. This made the floor noticeably warmer since we decided not to skirt it.
Where all the pipes come in and out of the house I sealed the gaps with expanding foam. There were 6-inch holes drilled for 2-inch pipes everywhere I want to keep the cold air and animals out.
This photo is under the shower in an unseen area. Anywhere that could be seen I trimmed the foam flush.
Now moving inside, all 4 roof vents had insulated cushions in them. Some moisture was building up behind them so the wife wrapped them in white plastic bags to stop the cushions from getting wet and possibly getting moldy.