Up until now you have not needed to be a member of any naturism association when you enter the resort. This seems to have changed though from July 2016 because several people have been refused entry for day entrance. If you are staying in the resort i.e. have a booking then you should have no problem. If you are planning to stay outside of the resort though and enter on a day pass then the advice I would now give is that you should have a FFN card with you and you can buy one here.
To enter the camp site, if you are not a member already of the FFN (French Naturism Association), you will have to pay for membership. Again, this does cost something like twenty or thirty Euros each and you can do this as you check in inside the camp site. If you have a camp site booking, then you can purchase the FFN card on checking in.
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