The button probably turns on the tank and pipe heaters. If the heaters are turned on you must have water in the tanks. Be prepared to use a lot of LP gas to keep warm, also make sure that you let excess moisture out of the RV (moisture from showers, cooking, etc). A small electric heater can also help in keeping the RV confortable.
2013 Prime Time 230 FBS
Days camped in 2013: April to November
Days camped in 2014...about 40
Days camped in 2015...more than 2014!!