What time of year are you looking for?
For open all year I've looked at a number for transit to Spain. There is a big one (name escapes me) at the top end of the ring road on the airport side, but is was a total disaster in terms of access from and back onto the ring road (despite what the CC book says).
In a few days I'll be at the site at Creon to the east which again comes highly recommended, but I'll reserve judgement until I get there.
There is another to the sought of the town, but looking at it on Google Earth its a no no due to limited pitches and access.
Sorry to be so negative. If others report good sites, particularly if open in winter, I'll be very interested to read.