Bill
I believe nothing for the bottom of the door
BUT i have heard a lot of water gets kicked up by the front tyre that then travels inside the front clip and past the door hinge and finds it's way onto the door sill.
A suggestion was the brush material they use over the wheel arch of atriculated trailer, and, when fitted to the chassis (Brush sticking out towards the side of the front clip, forms a "semi barrier" with the clip - with about 90% of the water then falling into the wheel area and not finding it's way to the sill and carpets.
I have not yet found the material but it sounds like a good idea in the damp UK
Ian