Hi Petra
If you're not familiar with Camping Cheques and the ACSI card then it might be worth having a look at the websites.
www.campingcheque.co.uk and
www.campingcard.com - lots of people on these forums use either one, or both. There are lots of other sites and also worth having a look at is the Caravan Club Europe 1 book - which can be ordered by non-members, or Le Guide Officiel Caravanning Camping, which is in French, but contains almost every French campsite including the smallest. This can be ordered from Vicarious books.
Le Plein Aire de Chenes at Clapiers is a Camping Cheque site, nearest to Montpellier, as is Fleur de Camargue at Aigues Mortes. We haven't stayed at either. You might like Le Mas de Reilhe at Crespian, which is a little further away, but a lovely small site and comes highly recommended. All these sites take Camping Cheques during June.
There are several ACSI sites - but again none of them where we've stayed.
We've stayed at a couple of sites at Le Grau du Roi (Camping Jardins de Tivoli which has private bathrooms on the pitch), Camping Eden, and nearby at Boucanet, Camping Le Boucanet. We've also stayed on sites at Remoulins near the Pont du Gard, which is easy distance to Montpellier, and I'd also recommend Domaine de Massereau at Sommieres (which I think is a Touring Cheques -
www.touringcheque.co.uk) site but only earlier in the season.