How do you repair rusted ford k a sills?

Depending on how bad the rust is, your best bet is to wire brush the rust down to the metal, a drill and wire brush attachment is good for this. If the rust has gone through, then this will need to be filled ( p38 body filler is one I have used before). Treat with a good anti rust paint, then paint back to original colour - this dose not nave to be a good match as the sills are not easily seen from a standing position. Hope this helps...