You should also look into sacrificial zinc, especially if you plan to leave the boat in the water. Zinc is less noble than aluminum or stainless and will absorb the worst of the galvanic reaction. In time the zinc will deteriorate and can be replaced. There are usually parts on the lower unit of outboards that are made of zinc and are easliy replaced. You can also buy a block of zinc and wire it to the boat to toss overboard when at dock (an example here). Always keep your motor out of the water when docked which will also reduce or eliminate the problem.
