Winter weather, short daylight hours, snow or rainfall on the panels, and nightfall all conspire to reduce charging from solar panels.
Best solution, IMO, is to just carry a wrench with you, park the rig with the batteries charged, then disconnect the two grounds from the chassis and house battery sets. Done. And the batteries will be fine after weeks of just sitting...assuming they were good with appropriate specific gravity when parked.
Takes all of 5 minutes and the cost of a used wrench from a thrift shop. Three winters in Fairbanks Alaska showed this works well.
