We always stay near there at Chateau du Gandspette, at Eperlecques, always using Camping Cheques. It's a busy site, with good sanitary facilities, pitches are generally OK (though do get waterlogged at times - but they are working on that by underpinning the grass with reinforcing), there is a nice small bar and a larger restaraunt area, where we usually have our last meal before catching an early morning ferry home. It's handy for both Calais and Dunkerque, and even better there is a Carrefour supermarket about 500 m away which is just large enough to do a last minute shop - and fair enough away from the day trippers to not suffer from the inflated prices of some nearer to the ferries! Cheap fuel, too, at the supermarket petrol station, so for us an ideal stop-over.
Without Camping Cheques, though, it can be quite expensive.