Protect mini-split condenser from ocean corrosion?
I don't know that there's much you can do to protect it. The condenser's job is to exhaust the heat from inside your home so you can't really enclose it.

Having looked around some, the only thing I've seen that's of a DIY nature is to rinse your condenser on a regular basis. Maybe rig up a sprinkler with a hose and let it spray the condenser. That should keep some of the salt out and hopefully prolong the life of your unit. Beyond that, regular professional maintenance was the other common suggestion.