A healthy battery will not need much charging between monthly uses as long as it is fully charged before storage. Simple cut-off switch attached to battery post should suffice, driving to campground will top off any minor losses if power is cut-off to your rig during storage. Obviously solar, removing batteries, and bringing genny periodically will work as well, your OP sounded more like leaving your rig in storage for months without power, a month or so between trips is something GC2 batteries are built to handle.