Think you had an unlucky experience; I have toured extensively in France over last three years with a large twin-axle van and have not encountered any problems at all. I am aware that France does (in common with much of europe) have a gypsy problem in some areas, and in some towns municipal sites and associated land does get 'taken over'. I always check a site entry in the Caravan Club book before arrival to check that it doesn't have a 'no twin axle' rule (some do), and also that there are no adverse comments about 'itinerants'. If there are I don't even think of going there. We travel off season and don't book ahead, but if you do it would be another way of checking you'd be OK on arrival. Generally I think there is more fear of problems than actually exists on this topic. It's important to look like a 'touring holiday caravanner' - hope you don't tow with a commercial vehicle as this won't help you at all! Just read-up ahead, and don't be put off by one bad experience.
Go back to France, and enjoy your next trip! Richard.