Chris,
I really like Northern Belgium, particularly Gent and Brugge, and on my commute home from Rotterdam nearly always stay in a family hotel in Damme (10 mins north of Brugge)
However, probably the best camp-site in Belgium is Camping Blaarmeersen in the "recreation park" just outside Gent - easy access to the motorway network and a simple drive to Brussels (or train journey)
Several others people from this forum have stayed there and really liked it.
If you want to research them for yourslef, the Dutch ACSI guide has a free web-site review www.eurocampings.net
Robert