Even 316 will crevice corrode, just not as badly as 304.
I think the Por15 will improve the corrosion resistance. It is impervious to water, so the metal will stay dry, means it wont corrode.
Por15 silver has aluminum suspended in the paint, so its good at coating and sealing holes. The base plate had some damage, so I used painters tape to back up the holes before painting. Por15 is very hard coating, like a hard plastic. But it is not UV resistant. To get hard and UV resistant, you have to buy RustBullet or MasterSeries Silver, Masterseries is a little more expensive then Por15. I figured its going underwater and to be covered with bottom paint so wont have UV exposure.
I left an electrical path to the base plate as I did not coat the inner hook, and I used a flat spade bit to remove the coating where anodes and cylinder bolts attach. I think the anodes will last a lot longer, if they have less exposed metal to protect. 316 is a little better than 304 regarding corrosion, the 2x4 SS sheet was about $140.
This time I got aluminum anodes instead of zinc.
If you could buy Duplex SS 2205 plate affordably then you would not have any corrosion. That new metal is very good for the sea water. High end boats are starting to use it as castings instead of bronze.
https://www.upmet.com/products/duple...ess-steel/2205
https://arcticsteel.com.au/stainless...-applications/