i wouldnt even use it unless coating osb i found some duraplate paint for the exact same price at sherwin willams (thanks jungle fever) i coated base but nothing else with a two part epoxy gel and painted over it does make a diffeernce will it stick ill know later.
the duraplate was 70.00 a gallon the fiberglass resin was 80.00 a gallon and a gallon will cover your dimensions.
Take into consideration that these are canadian prices not us so it would probably be cheaper out theire.
expensive mistakes are just that ex...............
i can give you the details on the duraplate later if you like its drinking water safe.