The only way you can keep salt out is with a hermetically sealed box or a HEPA filter. Silverstone makes the MM01, but it’s hard to come by (at least in North America). You could look into industrial cases for marine environments, but you’ll still want a HEPA filter.
Thought this was an interesting problem so down the google hole...
You can clean the salt off with >90% isopropyl alcohol. If you do that regularly your components should last a lot longer. It might even help the corrosion on your current board’s, so might give cleaning a shot.
They also sell spray-on solutions for these situations. You’ll have to take everything with a PCB completely apart and mask everything off before spraying, but seems like the best solution.
You can also submerge the build in mineral lil as
@milewski1015 suggested. Some people apparently watercool in a solid box and run the rads externally.
At times you'll have to use our sensors in a salt water environment. We show you how salt water affects electronics and how to clean them properly.
www.maxbotix.com
What are corrosion & water damage doing to your electronics? Learn how to remove corrosion from electronics and how to prevent corrosion from happening.
www.hzo.com
Lots of suggestions here:
I am fortunate enough to live at the beach and am a big electronic gadget guy. Almost every afternoon there is a solid onshore wind that blows in the house. The dust that comes off the beach ha...
superuser.com
en.wikipedia.org