The only thing I would add, is that if you are using a boat in salt, make sure you use an additive such as: Salt Away, Salt X or Macs when you flush your engine and rinse the boat/trailer. It's cheap insurance to keep corrosion at bay.
I personally use Macs when I flush the engine; as well as removing the salt, it's oil based and leaves a film on the water galleries etc to prevent corrosion. For the external of the boat, trailer and ski gear I use salt away. I ski most weekends throughout the year and usually get a couple of years out use out of a gallon bottle of each. So for less than $100 per year, you're silly not to use it.
Usually on an inboard (without closed cooling) that's seen salt water use, the first area to cause you problems is the exhaust manifolds as they corrode from the inside out.