I'd second everything Tim has said in his (as usual) helpful post. One thing I would add, is that France gets VERY busy in mid-July to mid-August during the French school holidays, and consequently there's more traffic, sites are busier, and supermarkets, markets and restaurants in holiday areas more crowded. France is lovely early in the season - most sites are open from mid-April onwards, and even the busiest sites can be idyllic then. In mid-May this year we had one whole area of a site to ourselves - like being in the middle of our own forest! However, in mid-July it's totally different, and some sites can be quite manic, so choose carefully if you're planning to be in France during this period. We always go outside peak season now, usually in May/June, and then again in late August/September, and use a combination of Camping Cheques and ACSI card to pay for sites - a good saving over the normal site prices.
The Gorges du Verdon are spectacular - but again, very crowded during July/August. We stayed near Castellane, at Le Camp du Verdon - however this was a few years ago now. On your way back from Perpignan I'd personally visit the Gorges du Tarn and Gorges du Jonte (and cross the spectacular Millau viaduct on the A75 north) as well as the Dordogne - a beautiful area, and less crowded than the Dordogne.
One tip, just like England, supermarket petrol is cheapest - but by a bigger amount than the discounts available in England. Don't try to fill up at supermarkets whilst you're hooked up though - as access (and/or exits) can be very tight.
Access to fuel in service areas is no problem, and service areas generally offer much better food than English equivalents. Supermarket cafeterias can be of almost gourmet standards (though not all, I hasten to add). We did have lobster once, near Frejus (could have been the Castellane trip).
Obtain as many guides as you can, to work out the type of sites you like the look of - and one of us on here will probably have experience of those sites. There are many of us on this forum who have years of experience of caravanning in France - and who enjoy sharing their experiences with others.