When you are bolting your boards in, make sure you face the grain cup so that it is facing down. Look at the end grain and turn it so that it is a frown. That way is will not hold water between the rings, but will tend to shed the water instead. If you haven't considered it yet, replace any questionable wiring and consider installing the wire grounded lights (the sealed ones with the 3 wire pigtail for the tail lights, two wire for the clearance lights) while the boards are out. Than all your grounding issues go away, as the ground is protected from corrosion.