don't know of any, but you could try Castells sites - they normally have lotsa facilities, March is awfully early tho good luck I think you're going to need it!
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But itīs all right now, I learned my lesson well.
You see, ya canīt please everyone, so ya got to please yourself
Ricky Nelson
Go to "http://www.campingwijzer.nl/", click on the Englisg flag to get it in English.
This online guide allows you to select on visiting dates. Somehow it does not work properly in Netscape, so use the Windows Explorer.
Select your region, set the dates and set the facilities you wish. You certainly will get a number of sites that are open during winter. Covered swimming pool may be a problem (expensive investment), but there must be some.
I'm not sure which part of France you mean by NE, but La Ferme des Aulnes in Picardy are open from the 26/3, with a lovely heated indoor pool. So you could have 6 days in March there!
Don't forget to leave a review of the French and other European campsites you have visited!