We had someone come to inspect it who said as much. We only noticed the problem after we had been out and about so it's on the 12v system.
We're on the Great Ouse and we're plugged in with a galvanic isolator.
It's all over without the raised pitting.
Since we've moved off the boat and stopped using electrics, it hasn't got any worse.
Everyone we've gone to has said it's galvanic corrosion. The suspicion is that, as the fit out was done by a previous owner, it was potentially done wrong.