Three-tread stringers coming down to asphalt driveway which slopes from right to left as well as being bumpy. I can make each stringer a different height ,at the bottom,but what happens when the asphalt changes its shape,again,in the future ? I thought about putting down a piece of PT planking for the stringers to rest on. That way they would all be the same size and shape and they could be shimmed,if necessary,at a later date. Anybody have any suggestions ?