With power electrical available cycle the inverter side of the Magnum MS2000 OFF and leave the battery switches ON. With the coach asleep for the winter you won't need the inverter in a ready/standby state to come online if case of a power failure.
Keeping the battery switches ON will allow the converter/charger side of the Magnum to keep the batteries fully charged. Check the battery water level from time to time the same as you would during the summer.
If you did not have AC power available then the battery switches should be switched to OFF.