France doesn't have 5 star sites - 4 stars are the maximum. Sites advertise in many places - try the Alan Rogers Guide (or the website), Eurocamp Independent, the Caravan Europe 1 book, the Michelin Green campsite guide (which highlights 'exceptional' sites in red), and websites such as www.campingcheque.co.uk, www.touringcheque.co.uk. If you go to any of the Caravan Shows there are always tourist organisations promoting campsites - and campsite owners themselves - and you can collect many brochures. There is a 'Guide Officiel' to all the campsites in France - which contains details of all 11,340 sites! The website is www.campingfrance.com - and you can order the guide from them - it's in French, though. So something for everyone.
Can't help with the route - we've not 'done' Santander, because it's always seemed so expensive. We prefer to take a cheap ferry and 'meander' down through France towards the south - heading towards where the weather is best, and staying there as long as the sun shines, then moving on. We usually have two 17 day holidays - and prefer inland France, with it's mountains, gorges, and so on.