You've still a huge area in the Midi-pyrenees. As your van is so long you may be better keeping off some of the (many) narrow, winding roads. A good centre, I think, is in the town of Millau. You get to see the new viaduct (well worth it), there are plenty of sites to choose from, and you're virtually in the centre of the area. You can visit the Tarn Gorges, the Gorges of the Jonte and Dourbie with all the wildlife, there are historic villages, caves, mountain passes, bastide towns, the vineyards of the Minervois are within a decent drive,and you're within about an hour and a half from the coast should you wish for a nostalic paddle!! There are some lovely sites in the gorges, but access is not easy to most of them.
In Millau (a market town, in a fantastic setting, but very much a working town, ie not prettied up for the tourist trade) you can watch the parascenders over the top of many of the campsites. I think a good one (improved over recent years) is Les Rivages - which is within walking distance of the town centre, for market day, yet has big lawned pitches, separated by hedges, with some right alongside the river Tarn, and easy access which will be important for you. There's a good pool, facilities are clean and 'wholesome', there's a bar and restaurant on site, and if you fancy a meal out you can walk into town where there are some excellent small restaurants.
Generally we love the area - and have been many many times before, both with our sons when they were small, and more latterly on our own or with friends also with grown up children. It's an area with plenty to offer for everyone.
If you're not tied to school holidays, too, it may be worth your while looking at the Camping Cheques website, or getting hold of an ACSI card (Les Rivages costs 14 euros at present rates, with an ACSI card). You can pick one up (probably) in your local caravan dealer for about