Camping International Aranjuez (ID:3721)
Camping Ciudad Zaragoza (ID:4106)
Have a look at the campsite database, depending on your route these are 2 excellent sites.
Aranjuez is south of Madrid and is approx. a 5hr. run beautiful palace gardens and town centre is fabulous with excellent indoor market
Zaragoza is only a 4hr. run, both are close on distance travelled 550miles from Santander to Benidorm. Free motorway from Zaragoza to the coast.
Bob