Motor homes with enclosed tanks. Fill on board. Disonnect city hose. Drain drain hose (Close valves first) live in it (run furnace) most are good down to 20
Trailers.. IF you have exposed pipes (Waste pipes) remember PURE water freezes at 32f/0c But what's in those pipes is anything other than PURE so it freezes colder If worried. DUMP in the heat of the evening and limit use after that.
Fresh system.. Same as motor homes.
Just now outside my door 34 and dropping (Was 35 45 minutes ago) rain turning to snow and I'm staying on the warm side of the door.