We are currently doing the opposite journey. I am typing this just north of Biarritz.
I spent quite a bit of time researching campsites which are open out of season.
There appears to be a few that are open all year, some close on the 31/10 and some on 11/11. So we are sailing close to the wind on some of them.
I have a spreadsheet with my research on if you would like a copy - send me a PM -
We haven't booked any campsites and have just shown up on the nights.
These are the nights so far:
Night 1 - South of La Rochelle -
http://www.campinglabrande.co.uk - on Ile d'Oléron. The Ile d'Oléron is a major campsite destination and is full of them - and muscles and oyster farms. The camp site is a little old around the edges, but people were lovely and has a heated indoor swimming pool and crazy golf - so popular with the kids.
Night 2 -
http://www.camping-bordeaux.com/ - camp site on the edge of Bordeaux so great location. Close to the city by not loud, but was busy - was full of motorhomes. Very clean and tidy. Appeared to have a nice restaurant but we didn't use that.
Night 3 -
http://www.camping-arcachon.com/ - in the Arachon Basin near the big sand dune. Very nice site with Nice pizza restaurant on site, again very clean showers and toilets
Night 4 -
http://www.camping-du-lac.fr/ - I am here now - again very nice site near a Lake. Has the best childrens play park by a mile, but other facilities are closed (restaurant/pool)
Next Plans are Biarritz, Bilbao and Santander. Most nights cost between 20 and 25 Euros, for 2 adults, 2 kids and the van - we don't bother with Electric as we are only one or two nighting.
Weather is pretty good, if it clear during the day then it gets cold at night. If you get a bit of rain then it is warmer. Generally 15-20C during the day. We pop the hearing on in the morning to help us out of bed.
Go for it.
Tony