I reserved a double room at a hotel for the festival Thursday to Sunday inclusive. I now don't need the room as I can stay in a flat near the island all week.
The hotel is in Samereau just over the bridge and back down the Seine a few hundred yards. It is walk-able from both the festival site and the main camp site. I can't remember the price but it is not expensive.
http://www.logishotels.com/fr/hotel-Hot ... 10817.html
Ring Chantal (She speaks English) - and help yourself!!