When on the Mediterranean we usually stay at Le Boucanet, near to Grau du Roi - just on the edge of the Carmargue. It's directly on to the beach, and clear (mostly) of mosqitoes. It has a lovely restaurant, shop, bar, pool, etc., but should be fairly quiet in September - and we may even be there - we usually have an early holiday (May, and then again in August/September). Flamingoes fly overhead at dawn, and in the evenings, and the sunsets from the rocks adjacent to the beach are spectacular. Grau du Roi is a small french fishing village, albeit with the usual tourist shops, but somehow manages to remain 'authentic'. There's a lovely route into the Carmargue by 'bac' (free car ferry) across the Petit Rhone - and St Maries de la Mer is worth visiting. There's no problem on a site like Boucanet, with itinerants, but there are a lot of 'travellers' in that area, so the smaller municipal sites may have issues. Stick to larger sites and you should be OK.
We've stayed in the lot, at Moulin de Perie - but the weather was unimpressive when we were there, so we moved on after just a few days. St Cirq Lapopie is worth a visit, as it the Grotte de Pech Merle (cave paintings). We visited another small town, Sauveterre la Rouerge, which is a Bastide (walled) town - and if you end up anywhere near, it's definitely worth a visit - the public loos, up an 11th century staircase are a talking point!
For wildlife you can't beat the Cevennes and Gorges du Tarn - vultures, beaver, butterflies, and birds of every other sort. Also canoeing..... oh I could go on and on......sorry!