We stayed at San Gimignano this year for one week on Camping Boschetto di Piemma. It is in the CC book and Alan Rogers. The site is within walking distance of the town which is a 'must see' for Tuscany. If you go, have a meal in the 'Villa Mura' restaurant where, from the terrace, you get a wonderful view over the valleys. The town is perfect for touring Tuscany, with Florence and Sienna within easy reach.
Lawrence