Both my last boat and my new boat have grounds to aluminum spars to power lighting, and over 20 years I have had a few ground issues. The base of the mast is at the back of the trampoline and is a very wet area, but ther have been issues a the spreaders and masthead too (the factory wiring set a poor example in many areas). Clearly we are creating a galvanic couple, going from copper to tin to aluminum (going straight from copper to aluminum would be worse from a galvanic standpoint). Some years ago, after a few failures, I went to cleaning the surfaces well and coating them with a very heavy grease/cosmoleen type product (just a tiny dab). No problems in > 5 years. No-alox would be another choice, more prone to wash-out, but better in other ways. Other, better, products?