We went to France in June and understand that out of season you don't have to book. Plenty of space on the site we went to, however be aware that they have a shorter season than us so check their dates and also they can be a law unto themselves and close early so don't be surprised if you rock up and they have closed for the winter!!
Have a fab time, very envious. Might be worth considering using camping cheques too, fixed price of £9.95 I think it is for unit and hook up and 2 peeps. Google campng cheques and you will find the site.
We have never booked campsites out of season. We use the Caravan Club Caravan Europe Guide (vol 1 covers France, Spain and Portugal) and Michelin, both of which are fairly accurate with their opening dates.
As you are in a campervan, you may like to use the camping-car aires situated in lots of the villages. I don't mean the aires on the motorways.
Have a good trip, I'm sure that you will have no trouble finding sites. We found plenty open in Sept/Oct 2004.
J&W
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Don't forget to leave a review of the French and other European campsites you have visited!
there's no need to book here if you want to come over, we'd love to see you. We're in the heart of the Loire Valley just north of Saumur, and a handy stop off point going south!
Mind you, next summer's a different kettle of fish. I'd book if I were you!