Re: plywood treatment
Sounds like you have CCA treated marine plywood there. As the 20 years of good wear has shown, this plywood doesn't need to be coated with anything to keep it from rotting. But, if you want, coating it with epoxy will help to preserve it further. The epoxy will also strengthen the plywood. A lot of guys here use epoxy from
US composites, probably cost $100 for a gallon of epoxy, hardener and pumps.