Personally, I don't think running
oil temps below 160F are much of a problem. The gauge might say that is the temperature in the pan but the
oil passes over parts of the block that are considerably warmer. Unless you do a lot of runs that don't get the engine up to operating temperature, I don't think water in the
oil will be a big deal. Change the oil at 2000 mile intervals if you're paranoid.
As far as the boat situation, they are rarely run for short periods and so water condensation in the pan should be very small.