I am currently looking into adding a wooden sub-floor to my crawl space. I currenly live in Gurnee, Illinois. Right now the crawl space area is coverd with gravel (lime stone?). Could or would it be possible to add a sub-floor out of wood using 2x6, 2x4, 5/9" Plywood and cover with a thick plastic for moisture, etc. Can you please advise. Thank you!