I'm no expert, but I think reusing the old skin might be too much trouble.
Go to FIberglassmans site. Fiberglassman.com
He replaced a large section of his floor with marine plywood squares and put a few layers of mat on top. There aren't any finished pics , but the next steps would be to fair level with a compound like quickfair or some other fairing compound (depends if you are working with polyester or epoxy). Finish the repair with gelcoat or 2 part Polyuathane paint. Then fix the non skid . . . Tape off the stripes and match the original height and skid pattern.
You'll be good for another 30 years
