I worked in water treatment for 30 yrs. We used Never sieze on bolts that were outside in the weather. Years after putting things together, they just unbolted very easy. Surface rust fell off and the bolts just unscrewed. I put this grease based grafite mixture on all metal/metal surfaces on the boat. Any excess wipes off. You can buy it in most hardware stores. The brand name "Never Seize" is what I use but alternatives are around. Keep a can on the boat.

Sandy