Got it!! Thank you sir! Always learning.
Yes sir...bondo will absorb water but when undercoated with an epoxy to block moisture from behind and then top coated with a good enamel or lacquer it should be fine above the waterline for small nonstructural repairs. That said... I use the word "bondo" but in reality it's not the best body filler for marine applications. Their is a product by Evercoat for tin applications. It's a filler that works better in wet environments above the waterline. It contains a zinc type promoter that helps with adhesion and also helps keep moisture out. A proper undercoat and a good top coat are still essential.
I've also read about an epoxy type body filler that goes on like bondo but is extremely water resistant...not sure of the name and I have no personal experience with this type of bondo but I read that it works good.
Thanks again for answering my question.