I would strongly suggest marine grade materials for the repair. Return what you purchased to the store.
I would lean towards tearing down right to the skin and installing marine plywood as the sub floor.
On top, I'd use one of the non tongue in groove plastic (thick version) floors.
Consider adding a heated floor.
So, make a sandwich:
finish floor (thick plastic NOT tongue in groove)
floor heating
marine plywood
insulation (silver foil)
seal at edges with great stuff or similar foam.
This is a job that will only be done once. Do not skimp on materials cost.