Enclosing a screen porch

Hello, I have a question about a project I would like to work on. It is basically enclosing a raised screen porch. The porch floor is currently a tongue and groove cedar (approx 30 +/- years old) with about 4 coats of paint on it which sits on 2x10 joists. Working down from there, it is insulated with paper backed insulation, then enclosed with pressure treated plywood underneath. The bottom of the structure is approx 3-4 feet in the air. My question is, I want to put down oak hardwood floor and I just want to know as far as moisture, mold, etc, what is the best thing to put between the cedar and the oak floor? Thank you in advance. Regards Chris

Chris, I would install a layer of 15lb felt paper (suitable for hardwood vapor barrier) over the cedar, then I would install 3/4" tongue and groove plywood (glue and screw), then glue and nail a quarter sawn oak floor to the plywood.  The quarter sawn will be more stable in areas that could be exposed to higher than normal moisture conditions.  This type of installation has been done in similar situations as you describe and has worked well.