I want to install a T&G porch floor over a 3/4 " CDX floor on a screened in porch. During heavy rains water does run onto the porch and puddle in areas. How do I prevent water damage to the floor? The 3/4" floor is just painted with water proof paint. I don't want water to get under the T&G 3/4" treated floor and rot the sub floor. Any suggestions?