Campsites at Les Sables D' Olonne - Vendee region

[Grr]

Hi after reading the posts about campsites at La Rochelle I am hoping that someone can help with our search. We have yet to venture taking the camper van to France and I am trying to persuade my husband that next June for the half ironman triathlon this would be a great opportunity to compete and camp. I have done a couple of google searches for campsites and found it very different to English campsites. We would like to camp v close to or in Les Sables d' Olonne as the triathlon starts and finishes in the town and with an early start and 70miles to cover don't want to have to move much afterwards. We also prefer quieter camp sites with good toilet/shower facilities. Also then trying to persuade husband to extend it into a holiday afterwards as long way to travel from Devon for a weekend of racing. Would you move campsites or is it a nice area to explore? Finally sorry to ask so many questions on the websites I have come across there doesn't appear to be the facility to book or check prices for next year, as over 2,000 competitors take part we need to book a campsite.
Many thanks in advance for the help.