exterior chain plates
There is a post in the Reliance forum "What numbers are there?" on September 14, 2009 from "svbornfree" (in South Carolina) stating that he or she "is going to go to external chain plates".
I think that's a very good solution to the problems you mentioned. I think this is a classic question that sailors grapple with -- lots of posts about this topic on the internet. As far as I can tell, the only downside to external chain plates is the appearance. It is much easier to inspect the through hull bolts on an externally attached chain plate.
I figured it was a big improvement to replace the exposed soft steel with 316 steel. As for the fibreglass embedded steel, after replacing it with 316 steel, the best I can do for the next 20 years is to make sure the places where the steel enters the fibreglass remain well sealed.
My current thinking is that whatever solution each of us adopts needs to be carefully checked each year; and it's very important to check every place where stainless steel ceases to be exposed to air and either make sure that spot is well sealed (to prevent water penetration) or, if possible, remove or uncover a portion of the unexposed steel to examine it.
Kind regards, John