My house is ca. 1927, located in Northeast. I would like to replace the tongue and groove decking on my front porch.The porch is fully enclosed on two sides, partially enclosed on the other two sides (with three foot walls) and is covered with a roof. The porch is over the front corner of the basement, so the replacement decking and subfloor must be waterproof. The current decking is painted and peeling (and contains lead paint -- yuck). I am considering T&G mahogany, but my research indicates that this is a poor choice for watertight applications (and with no air circulation beneath). My questions: 1. What T&G decking material might you recommend? If I use mahogany, should it be sealed on all six sides and with what product? 2. What type of barrier should I install between the joists and the decking to make the decking waterproof yet inhibit deterioration of the decking? 3. If I find there is damage to the subfloor or joists (some of the current decking is loose at the edge) should I use plywood for the subfloor. Any other tips appreciated. I am concerned about doing this work and then having cupping or warped decking or water penetration to the basement. Thank you.