Most of the problems happen when your connected to shore power and don't have a galvanic isolator.

We didn't have one at Crews Inn, Trinidad and in 4 months it ate up our tube stack and aluminum housing. We had to buy a new tube stack and have the flange on the manifold housing re-machined. $1,100.00.

We added a galvanic isolator and the corrosion has been cut down by about 90% since then. We still walk around the dock and make sure other boats near us don't have their shore power cables hanging in the water. Some say it doesn't make any difference but I disagree, besides, it's sloppy seamanship.

Our boat is on the Rio Dulce at present and we have it disconnected from shore power. We have an air-conditioner (working as a de-humidifier and temp regulator) in the companionway that is hooked up directly to a feed from the dock keeping the boat 'offline'. Sure it's fresh water but I'm not taking any chances.

Keep your boat disconnected from shore power and you should be fine.

At least that's my take on the problem,,,, as poor as it is.