Tell us how much time passes before replacements. Many would not be concerned with what the pictures show, but sounds like you are very diligent. A couple tricks I use. Sometimes bathe the outside of your battery with a mixture of baking soda and water and dry it. Keep the battery top dry. Metal hold -down brackets and screws are conductors and tend to promote corrosion. I make my brackets out of plastic. Try cutting one out of large dia PVC pipe. Stopping corrosion entirely is impossible. There are something like 11 kinds of corrosion. Most common is with liquid electrolyte (water . acid) connection, but moist air also serves. It does seem you have an active case.