Thank you Tony for recommending Just Go.
I've put your campsite query on our Facebook page to see if a wider audience might like to comment.
You might like to head to a bookshop to browse through the Alan Rogers Guides. And take a look at the France Passion stopover scheme online: http://www.france-passion.co.uk/
To get discounts at campsites in Europe take a look at the ACSI CampingCard scheme: http://www.campingcard.hu/hu/en/europe/
If you fancy a quick, cheap nightstop with basic facilities, try out the network of aires throughout France and Spain.
http://www.eurocampingcar.com/carte.php3?langue=uk&lcCarte=1010000&h=1360751475