I've had to change out a tank. Twice in a lifetime of
boating. I might have changed an element once, but that could have been someone else's
boat. I've never seen semi-rigid pipes for the engine jacket water loop from a water heater, but I suppose that could be describing the normal hot and cold domestic water piping, which frankly I find a lot easier to
work with than back when we had to sweat copper pipes in the house.
As for scalding, I never understood that argument, either. Doesn't your faucet have two taps? If the hot is too hot, add some cold. Personally, I love the option to use scalding-hot water to quickly wash greasy dishes and such. But I did eventually cave in and add a thermostatic tempering valve. Mostly because it saves on hot water.
I'm not really sure what my point is here. I guess it's just that, of all the frustrations from maintaining a boat, the water heater has never been high on my list. Oh, and a tank of hot water can last quite a while without any
solar,
battery, engine or genset input. I like having hot water without any immediate power management effort.
But... it's your boat. You set it up to your specs. And let us know how it goes, maybe you'll change my mind!