From the 15th of August various carparks in the forest will be closed at night, ie Franchard, Épine Nord and Épine Sud, Grands Feuillards, Rocher Canon, Apremont and Cabaret Masson (
http://www.fontainebleau.fr/?foret-de-fontainebleau,2149).
That doesn't mean van and camping-car owners should stay at other carparks as it's not allowed either, and since the beginning of the year there's even a signpost reminding drivers of this at various carparks (Vallée de la Mée, Croix Saint-Jérôme, JA Martin too I think). Use the free aire in Milly or the free and legal bivouacs around the forest (Bourron-Marlotte, Bois-le-Roi).
Something tells me that's going to make a lot of people unhappy!