The number one failure cause of the bottom of the siding I see around here is the failure to properly paint and seal the bottom of the wood panel and several inches of the backside. I've seen some done right, with the bottom and several inches up the back side properly sealed and painted, that are real old and still doing fine. I've seen some not done right, no paint or sealer on the bottom and several inches up the backside, that rot in just a couple of years. -