Reading these two paragraphs in your posting makes me wonder why you
didn't take the opportunity to replace the wet balsa with foam core
I definitely considered it and looked at some other materials but decided to replace the core with what was there before. Based on my research balsa core is a superior core material. As long as it stays dry. I understand that even some of the foam and high tech materials are subject to water damage eventually if any gets to it. No matter what core I use keeping water out sounds like it is key. Balsa is an excellent core, is easy to work with and is economical.
You will regret the things you did not do, more than the things you did.
Get out there!
Saco Bay, Maine
2001 Beneteau Oceanis 361