Wak,eboard boats and saltwater

Is closed cooling a must? Galvanized trailer, anything else I need as an option to protect from the salt water? Thanks.

Yes closed cooling is a must ! So is the Galvanized trailer. Get a flush kit for your brakes too or you will be replacing them yearly.
I had a Fishing boat for years that I used in the ocean so I have a good idea of what salt will do.
Pay a little more now or pay a lot more later!

Closed cooling is not a must, it helps but is by no means a must. I have been skiing in saltwater for 20 years. Things like exhaust headers will rot quicker in the salt but you should get 7-10 years out of them before they need replacing which is not much less than fresh. I know of a 78 mastercraft which has spent all its life in the salt and still on the same block.
Just flush after each use and wash down and it'll be fine.

Brake flush is a must. or if you have a big enough rig, just don't get brakes.

Well with in 5 years I had to replace the exhaust risers and the manifolds were on there way out too.
The thermostat and housing was also a problem.
Not to mention what is going on in the water jackets, as they corrode they clog and the water volume will decline.
You can have one cylinder running hot and not even know it.
I would think that it would be even worse for a ski or wakeboard boat that has heavy loads on the engine.
Can you run a boat in salt for 10 years with out closed cooling ? sure but it will be junk and you cant rebuild it.
My suggestion is ask a couple of marine mechanics and see what they say.

i run a 94 prostar in salt water, just make sure u flush after every use, and if u notice 1 cylinder getting hot, its most likely crud build up, i had this problem, so i ran some high end german engine flushin and clean through the boat, got alot of gunk out and boat runs fine
So just know that with salt u will have alot more work but hey do what ya need to getout and ride.