Personally, I'd be happy with Waxoyl.
The problem for the ash frame is water ingress both underneath as well as from above via the trim under the door. I don't know what Morgan use currently but they used to use horse hair as padding - an absolutely wonderful medium for absorbing and retaining moisture.
The trick for ash frame longevity is protection from direct moisture, preventing the conditions and growth of wood rot and ensuring that it remains as dry as possible.
