Hello, i am a local kiter at leucate, btw i dont get the point to speak about Lyon, it is quite far from Leucate, but yes you should avoid sleeping "on" the highway.
Dosses is now reopen for kiters but its not my favorite spot as it is not "sandy" but more "rocky", to find the best spots you can go to the dosses and from there you can see where are the other kiters.
Sorry i do not advertise about my favorite spot as it is my hidden gem ^^ But i found it looking far away kites from dosses spot.
Please notice that Tramontane is a gusty wind so put a smaller kite then what you think, Dosses was closed because of fatal accidents.
Also you have a big kite event named Mondial du Vent in April : http://www.mondialduvent.fr/
, can be great to ask around or meet some kiters.
Please note that there is no ocean side there but Mediterranean sea side
Anymay Leucate is really a great spot to kite, kite safely and have fun !