I am in the process of enclosing a large roofed porch at our home in northern PA, using large insulated glass units installed between existing 6x6 posts. I plan to lay half-inch OSB sheets on top of existing decking, with vinyl flooring on top of that. The porch sits about 3 feet above a dirt surface. The enclosed porch will not be heated but will be used much of the year as a sunroom and will likely experience major temperature swings and possible condensation challenges. Should I place plastic sheeting between the existing decking and the OSB subflooring? Should I also place plastic sheeting on the ground beneath the porch? Any other advice regarding moisture/condensation?