Just got back from La Yole. I do not think there is much availability now for August - someone on the site was trying to book to return in August and managed to get in. I would suggest you contact them immediately by email which can be found on their website. The last two weeks in august are generally quieter in France than the first two as this seems to be when the
French take their holidays. Their seem to be two areas to the site, on the left as you enter are well shaded (probably too many flies) and on the right there the sunnier pitches. I would not recommend you chose a pitch on the outskirts of the play area. The pool complex is very nice but not too "dressed up" so as to attract those requiring a more "lively" holiday. Restaurant and bar area is very good and clean. The local beach at Les Mouetts attracted a few flies when we were there as we did have a few good downpours of rain and this seemed to bring them out. We found the beaches better at St Jean de Monts or St Hellier de Riez - you did have to go by car but then again, unless you wanted a long walk carrying everything with you, wou would porobably take the car to Les Mouetts. No parking charges anywhere. Supermarkets in St Jean de Monts are Super U and Intermarche which were of the usual good standard.
If you cannot get in at La Yole there were many other sites local but appeared much more lively - Le Clarys Plage, Les Genets, Zagarella etc.
Get booking straight away! If you are booking thru Caravan Club it may be that their allocation of pitches has already been taken so you will have to book direct with the site and book ferry separately. You may get a good deal booking thru Camping Cheques for the ferry inclusive of 3 free camping cheques which you can use later this year or next - they may be able to used towards the end of August - just check with the site when low season begins.