If you have a soft spot in the floor you might also have other hidden damage. Before you close the hole up check to see if there is more damage that needs taking care of. If you go to Bateaus2.com they have a forum that among other things covers repair under
Cracker Larry's Corner: Boat Repair and Rebuild Support
There are a lot of people that post pictures of the repairs as they do them and you can get questions answered. If you join the forum (no charge) you can post pictures of what you are looking at and get recommendations in what to do.
I built one of their boat designs and used 20 gallons of epoxy and yards of biaxial fiberglass. I live in Sulphur and if you have any questions PM me.