We just recently enclosed the open crawl space under our weekend cabin to provide for more enclosed storage. We went with 6X6 green treated timber as the footings for all the exterior walls. They sit on a 6 inch bed of crushed stone and are pinned into the ground with conduit. On top of that we built 2X6 green treated framing and to finish it off we applied green treated plywood as sheathing material. I would like to apply additional sealer to the bottom 10 or 12 inches of the plywood to provide added protection against moisture, etc. I have seen all types of foundation sealers, tar, black jack, etc, but am not sure what exactly to use. Can anyone suggest the right material to use for this? I do realize that the wood is already pressure treated but wanted to add to this at the grade level. Unless of course this is a no-no in which case i will just leave it alone. Any suggestions or advice would be appreciated.