Jonathan, thanks for the great reply and info on the campsite and launching etc. Thanks also to John for those fantastic photos! We have booked for the summer now, but will definitely be pencilling in this region for the future, it looks superb, and we are very green with envy that you are fortunate enough to have a house there!
We have settled on Argeles sur Mer which is very close to the Spanish border with France on the med side, and we believe it to be very picturesque - once south of the very long sandy beaches. We think that it is possible to launch at the harbour there - although emails to tourist office are as yet unanswered! The campsite "Camping La Marende" is more than happy for us to keep our boat there, and although there is no launching from site, it is very close to the beach. The kids are very happy!
I shall try to post our experiences - which will hopefully be great - on our return, but until then I hope everybody has a great summer.