Caravan storage sites in France

We are thinking about finding somewhere to store our Caravan in France next year and wondering if anyone can reccommend a storage site or give us any advice on this.  Ideally we would like to take the Caravan to France at Easter  and leave it there until September or possibly even all year.  We would either like somewhere midway on route to the South or somewhere in the South that would give us options for different areas to visit.