Advice on open sites France in March

We travel to the south of Spain in March. We used to stay over near Tours at Camping Les Acasias but they don't allow a twin axle caravan. I have struggled to find anything open that time of year. We usually stay over an hour from Calais on the first night, then around the Tours area and from there to Urrugne on the border with Spain. Any advice/suggestions greatly appreciated.