We're in Clackamas, KC. Our coach has been stored uncovered next to the house most winters for the last 8 seasons. I turn off both battery switches and allow the solar panel to keep the batteries up. I keep an eye on the water level in the 4 house deep cycle batteries, usually adding distilled water 3-4 times a year, more often if the coach is used much. I monitor the Magnum inverter panel over the entry door, especially in the winter when solar input is minimal, and like to see around 13.2 volts.
If the solar seems to be inadequate, which is rare, I may plug the coach in, and I do anyway if I opt to use our electric air dryer to help restrict any potential for mold growth. Of course the solar aspect is lost if you decide to store inside, but your coach won't require as much attention to keep clean. Our batteries all seem to relish the routine, factory originals and still good. If you store inside but without power, I'd disconnect the battery cables to prevent parasitic drains that your main switches don't affect.
Joel