4 Season RV (as advertised by various mfg.s)
Enclosed & heated underbelly (typically a duct run into area around tanks/valves from furnace-------better would be that AND heat pads on tanks)
Block insulation
Attic vents
We spent several weeks during our travels in below freezing temps (mid teens down to -14*F)
Stayed warm, used on-board water and no issues with frozen tanks/valves.
Colder it got the more when had to leave cabinet doors open at night to get warm air into nooks/crannies
PROPANE.........if set up on site (no travel) look into 100# set up by local propane dealer.
Got old taking a 30# to get filled every other day