Dan,
I work in Rotterdam, living in the UK and Brielle (Holland), so if I can be of help, I'll try.
Good campsites - take a look at the Dutch ACSI web-site and look for 4 star sites - if top quality is wanted (Caravan Club or better - often on-site restaurants) or beach sites or "Green Camping"
http://www.eurocampings.co.uk/en/
But we like:
Gent (B) Camping Blaarmeersen (4 stars) - probably the best camp site in Belgium - good for centre of Gent and a short drive to Brugge
Brugge (B) Camping Memling (2 stars) - closer to "caravan and camping club" standards - utilitarian toilet blocks
Delft (NL) Delftsehout (4 stars) - town centre site (like York or Bristol CC sites in the UK) which can easily get busy, but has all the right boxes ticked - easy walking access to town centre - loads to see and do - easy walking (or bus) access to Delft train station and easy access to Amsterdam, Rotterdam, Leiden, etc.
Plus the "Green Camping" sites south of Rotterdam, along the north sea coast, down to the Belgian border.
Plus - we are rebuilding the Eriba Owners Forum - and I've posted two reviews on Belgium and Holland on the new test web-site - follow this link and most of the internal links are active too:
http://eriba.jconserv.net/viewforum.php?f=20&sid=6af6d8ec434433432e1fe3154de95440
Robert