I should have known initially to be more specific and clear. That's why I love this site. Always great analysis and advice.
1. Too difficult to cut out as it's in the fiberglass lip area. It's on the extreme back edge of the burro
2. Area is "6 out of 10" for deterioration. Not critical but clearly soft.
3. Wood is dry and window no longer leaks
4. Already have possession of RotFix
My question should have been "if I drill holes through the fiberglass and inject RotFix will the wood bond permanently to the fiberglass, making separation impossible if I ever want to replace the floor."
Thanks guys, for the interest and help.