Helen
We tend to use Gandspette in preference to la Bien Assise as we main come from the south. However we might use it is Septembers as we will be returning from the west. There are quite a few campsites around Calais the troube is that they will also be busy as its the peak time. Bein Assise might be the best bet as they have a lot of transit visitors so if you can arrive early you could be OK. If you look here http://www.davidklyne.plus.com/european_campsite_index.htm I have several reports on campsites in the Calais area that might help.
David
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