Obvious from the title, looking for recommendations for few nights in Font?
This campsite looks good. All facilities and a reasonable price:
https://www.fontainebleau-tourisme.com/en/file/5185338/camping-municipal/
https://www.campingiledeboulancourt.com/home/ is nice
Free aire for campervans/motorhomes in Milly. You have to press the button to lift the barrier.
Aire de Camping-car Communale de Milly-la-Forêt+33 1 64 98 80 07https://maps.app.goo.gl/zhRu9QV95sr4R1Zc6
Outline of where *not* to park, from a Fontainebleau local:
https://www.instagram.com/p/CdDYX1Es8Z3/?igshid=YmMyMTA2M2Y=