La Bien Assise at Guines is about 10 minutes from junction 14 (note that the junction numbers have now changed). It is a Castels site. Nice pitches, pool etc. Good for an overnight or a longer stay. http://www.les-castels.com
I agrre with Mike that La Bien Assise is a good campsite but so is Le Chateau de Gandspette, have a look at these two links http://www.davidklyne.plus.com/CampingLaBienAssise.htm andhttp://www.davidklyne.plus.com/ChateauduGandspette.htm