We went to Chateau Drancourt (on a MN prize 
).
The area is excellent, especially if you are quite outdoor people. There is a fabulous circuit of cycle pathways all round the Baie du Somme, which has a couple of small seaside resorts and miles and miles of wide open beaches. The area on the Northern side of the bay has a bird sanctuary, a fabulous area, and I think there were some more 'field, dunes, and a toilet block' type campsites around that area, and also in an area round the southern side of the bay, bizarrely called something like 'Brighton sur les Pines'. St Valery is a fantastic v small town, pretty, a lovely promenad of restaurants along the estuary, some lovely ancient streets, two good markets for fantastic fresh produce as only the french can do. Trips out and about included a fascinating underground city built in caves at Naours.
Le Touquet (Stately traditional resort) and Bagatelle theme park within easy distance, and Amiens with it's fantastic cathedral.
Chateau Drancourt would be a good base - it is quite 'holiday park' like in camping terms, and I would imagine the pool is completely heaving in sumer. I did look in the shower and washing blocks (we were enjoying the comfort of a mobile home) and the facilities looked excellent, esp the washing machines etc. And the site was really pleasant.
Lovely beaches on the bit between Calais and Boulogne at Wissant, Audreselles is a lovely small seaside town.