Freddie,
Go! We went in February this year for 6 weeks. Stayed on Costa Blanca.
Took P&O Dover Calais (cheap) then stopped Rambouillet (site opens 1 Feb) but you can stay at Dreux (site in Caravan Club European Guide). Next stop Orcet near Clermond Ferrand (open all year) then Narbonne (La Nautique opens 1 Feb but there are others open in January - see Guide). This route saves lots of tolls on French Autoroutes.
Then Barcelona - Vilanova and to Costa Blanca next day. Nice trip, no problems safety etc. Plenty of sites open in Spain and good rates with Camping Cheques or ACSI card.
You can go West France, N Spain to Valencia but not many sites open in inland Spain in winter. We stayed at Calatayud on way back. Difference in distance was only about 50km!!
We're going end February 2006 for another 6 weeks. Can't wait!
Alan