It is 2 degrees where I'm at right now. I leased a 100 gallon tank for the winter ($45). I've filled it up 3 times now. Advantage of a big tank is the delivery guy charges me the same as a house, so far roughly $1.50 per gallon average. Can't imagine trying to winter paying the RV Rates ($3.39 last I checked, but that was before the drop). At this point, using a lot of propane is still cheaper than relying on electric heaters (my neighbor's electric bill was $240 for 30 days).
I'm not sitting on a nest of hay (not allowed here). I can 'box in the bottom' if I cover it with tarps. They won't let me use the silver foam insulation ("looks tacky"), so I'm living without. While it would help, the really cold nights are the exception here, with lows usually in upper teens and twentys. It is the cold wind which defeats the heated water hose, and that is usually at the connection, despite the insulation attempts. Keep your lower cabinets open and air circulating if you are worried about your tanks, and disconnect water supply during the coldest snaps.