When you say 'South of France' do you have a particular region in mind? There's the Riviera or inland a bit Provence, the Camargue, the Cevennes mountains, the Ardeche, the Languedoc/Roussillon, Midi-Pyrenees, or the Atlantic coast by Biarritz. I've seen them all described as the South of France.
Most people mean the Riviera/Cote d'Azur - which is the most crowded part in July - so perhaps consider inland as Other Clive suggests.
It depends, too, what you want from a campsite. Do you have children with you? Do you want a large all-singing site, with bar, restaurant and entertainment, or would you be happier with a smaller site with basic facilities. Do you need to be near a beach, do you want surfing or boating, or a river to mess around in, or a lake? All these are important in offering recommendations. If you could give us a bit more information I'm sure you'd get lots of replies and suggestions.