The outside I wax with auto wax and the inside I keep a silica box ("Browning Dry Box") to take the moisture out of the air. I regen it in the oven annually. I also take everything out twice a year an lightly oil and run an oily patch thru the bores. Never had any issues.
Many use the Golden Rods which are probably better but I never bought one as we winter in Texas and I leave as few things plugged in while we are away as I can.
I feel the main protection is to keep your guns cleaned with a light coat of oil.