Hi James
We have stayed overnight in our caravan in the car park adjacent to the Norfolk Line Ferry offices at Dunkerque several times. Most recently we stayed outward bound on the evening of Sunday 25 July having arrived on the 6.00pm boat from Dover. In 2009 we arrived there at midnight the night before we were due to catch the 8.00am boat the next day. We awoke early and queued for and got on the 6.00am boat instead, no extra charge.
There are always plenty of other 'vanners overnighting in the car park. We have never had any problems staying there as the port is well away from the town, etc. There are loos and a snack bar in the adjacent NL offices but certainly the latter is only open during the daytime, no sure about loo access.
Last Tues-Friday on the way home we stayed at Chateau Gandspette for 3 nights as we had to take our dog to the vet for his pet passport to be completed. Chateau G are open to the end of September. At c£28.00 per night I feel Chateau G is very expensive and trading on its convenient position for the ferry ports. We will NOT be staying there again.
In 2008 we stayed at Camping Parroquet on the coast near Dunkerque the night before catching the boat home.. You can read my review here:
http://www.ukcampsite.co.uk/sites/reviews.asp?revid=8173
Hope this helps
Tim