Appropriate fuse for 12V battery - solar power controller connection
Just to follow up on this: the project is over now without any fuse-related mishap.  I deployed about 40 systems and for most of them I just used in-line auto fuse holders with 20A fuses, purchased from radio shack or auto parts stores, on the positive line between the battery and the solar controller.  Occasionally fuses were blown, but rarely.