Have you worked out which route you'll be using? There are so many alternatives that it would help to know which roads you're planning on using before recommending sites. You can use one of the route planning websites such as mappy.com, or viamichelin.com to look at alternatives, or do it the old way with a paper map (which is what we do). The tolls on the autoroutes can add up, and the route planning websites will calculate the likely costs for you - be sure to select 'with caravan' if you're towing as the tolls will be approximately one third more with a caravan.
We generally do Calais(or Dunkerque), Abbeville, Rouen, Chartres, Clermont Ferrand, Millau, Perpignan and then into Spain - but others recommend using the A20 and going around via Toulouse, then over the border at Bourg Madame. We've always had two overnight stops though, so we can arrive at a decent time to set up in daylight! We generally stay overnight somewhere around Salbris/Nevers and then again around Millau/or down towards the Mediterranean.