Spanish campsites

I am no stranger to driving in Spain and enjoyed the Paradores particularly in Asturias but for my first trip in the camper I intend to meet Sister who has lived in Madrid for 50 years in Granada and would welcome any tips for leisurely drive down from Santander. I am done with beaches after 4 kids and prefer quieter out of the way places. I am sure the advice will be that is best to book but is it possible just to turn up on spec?

What time of year are you travelling?

I am probably going in May June as the rendezvous at the Granada Paradore is end of May

Hi Snowy,
The aim - though by aim i mean first thoughts and may be the driving to chilling ratio is a bit much, is to go Santander Zaragoza Valencia Almeria Granada Cordoba Huelva than back up through Extramadura and along north coast vamping till time to return to Santander. I have seen Campingred website which seems to have a lot of campsites. Does anyone know this site? If so and are the featured sites all busy and big - as travelling solo so I would prefer small and out of the way! Cheers