Replace floor with??

[Starzofchaos]

Yes, Marine AB plywood is Douglas Fir. Not sure what the Big Box stores carry. Doing a quick search says you can even get marine ply wood at these places.
http://www.roseburg.com/Product/abmarine/

As for the Epoxy... I've used stuff that is expired before with no problems. Just do a test batch to make sure it work for you.