I thought I would show the quality difference between Marine grade Fir Plywood and regular exterior usually ACX. Well, one half. The marine grade is AB, it has more plys with 7. Almost gap free. It is said that it has same glue as regular exterior grade fir plywood but I am not sure. It is a full 3/4" thick and matches up with old floor in trailer other is 19/32nds. It cost my $70.00 a sheet . Probably. Anyway, in case you are trying to decide. I will be soaking edges with epoxy for good measure.