Possible places, please comment:
http://www.kampeerhoevekoole.nl/
Website only in dutch, 8 sleeping rooms for 2-6 persons, 36 beds in total, kitchen, close to lake
Public transport seems available via (cheap) taxi bus and train to Leiden
Added on Mon, Jan 12th:
http://www.mariajohannahoeve.nl/index-engels.htm
Kitchen and large living room available, 24 or 32 beds
http://www.seeburgh.nl/duits/index.html
Kitchen and large rooms, 28 beds, at the coast! Availability limited to midweeks?