Hi Sue
I have done it numerous times over the years and still find the best route is the west coast route via the shuttle, we get the early morning shuttle 06:00 and drive down to Pau then through Somport Tunnel down to Villamartin, I haven't done this route through the winter as the Road over the Pyrennes could get blocked but you can go via San Sebastion and Pamplona.
Basically Calais, Abbeville, Rouen, Le Mans, Tours, Poitiers, Saintes, Bordeaux here we tail off to Pau for the night, through Somport Tunnel, Jaca, Huesca, Zaragoza, Teruel, Valencia and down to Villamartin, or winter run as I said Bordeaux, Bayonne, San Sebastion, Pamplona and pick up Zaragoza route from there.
Hope this helps....
Regards
Andrew