Being occupied with propane heat has different risks than unoccupied with heat "off".
When the temperature of the water in the pumps, pipes, and valves drop below 32 degrees F, the water will freeze. How much protection these things have will decide how fast the temperature drops. It depends on where they are and if they are next to something that is exposed or not.
One place may freeze and other places may not. Full water tanks with some protection may take days to freeze. Empty or close to empty tanks may freeze, but rarely are damaged. Tank drain valve can be damaged depending on the configuration.
Water heater tanks are exposed to the outside through the burner. 6 gallons can take a while to freeze. Use a thermometer to see if yours is close to freezing. Keep heater "on" for below 32 degree weather.
Small water spaces like in pumps, pipes, and valves may freeze quickly. Dribble the water over a thermometer to see if yours is close to freezing.
The pump and pipes in the "heated and enclosed" belly of my TT froze solid in less than 4 hours at 28 degrees F.
I hear lots of people say "20 degrees for a few hours is fine." I also hear plenty of people who have to replace check valves, gate valves, pumps, and faucets who don't discuss their freeze protection policy.
I wish you good luck and happy trails ahead!