So, for anyone interested in my paranoia about boat batteries getting submerged in salt water, I found this thread on a another forum.
https://www.thehulltruth.com/boating...saltwater.html
Based on that, it sounds like you don't want your batteries to get wet, especially with salt water, but if you have them in a battery box, with the cover on and use the strap to secure the cover, I think you should be OK, even if you were to say... stuff the bow and take on a lot of water sea water.
It sounds like your batteries should still function well enough that you can run the engine and your bilge pumps.
That's great news to me. I may reconsider my plans to relocate my batteries towards the bow. The weight transfer would be good, but the long battery runs to the motor are a concern, as is the cost of good wiring.
Just an FYI for anyone who was concerned, like me.
It seems that salt water on the top of your battery will cause it to discharge, but it sounds like it won't conduct soooo quickly as to rapidly and violently discharge the battery the same way you would get if you shorted the two terminals together with a thick battery cable.