Hi Brum
The motorway routes through France or through Spain are both about 500 miles, so it's a matter of choice. Personally I would take the Spanish route - A8 then AP68 to Zaragoza (233 miles), AP2 then A2 to Barcelona area, then AP7 north (267 miles); total 500. They are mainly toll roads, but very good and quick, and the tolls are much cheaper in Spain than in France - and they don't charge for caravans. There is a new municipal site in Zaragoza (Camping Zaragoza - see web site), which opened in 2008 and is very good for an overnight. I stayed there a few weeks ago. France is quite expensive at the moment - reminds me of when I was young (and poor!!) in the 60s, when we used to rush through it to avoid the cost. Spain is much cheaper. Basic things like a coffee will be €1.30 in Spain and about €2.60 in France. A small beer is similar prices.
Unless you particularly want to go to El Delphin Verde it is about 180 miles less to go to Cambrils,same route, but turn right instead of left onto the Med coast. It is further south, with probably slightly better weather and some excellent campsites.
Hope I have been of some help.