If it were me I would go to P-N-P with a battery powered sawzall and cut that part of the floor pan out of a pu or runner. Cut the damaged part out and trim the piece to fit. Weld in in place or pop rivet. Get some body seam sealer and seal it up, and paint it top and bottom to stop it from rusting. That way you can run the stock 3-piece boot with the metal ring and not worry about it leaking fumes.