Being in the Netherlands myself I can tell you the Police has gotten really strict with enforcing the rules in the last couple of years. Even with a trailer for your boat there is a high risk of getting a ticket these days. Quite a few buddies of mine have gotten one when trailering to and from an event. I wouldn't risk carrying something like an A-cat on my roof with the way things stand now.
Wouter
What were the tickets for? <img src="http://www.catsailor.com/forums/images/graemlins/confused.gif" alt="" />
Is this something we should be wary of when travelling to the GC in August?