On my shed pouch it has Marine Plywood and there is some cracks where the top layer has some wood missing and I would like to know what to fill them in with? After they are filled in I am going to put Cabot Stain on the floor, should I put a Primer on first? The floor does see weather. I would like to get this done as soon as possible for I live in Ohio and Winter is coming. If you can tell me what I should use it would be very helpful for me. The stain is a solid color.