Hi Robert,
there was quite a good thread around this subject that is worth a read if you have not already found it;
http://wayfarer.org.uk/forum/viewtopic.php?f=4&t=893
Someone who used a weighbridge for their boat/trailer found it came in at 460kg
We currently tow our Wayfarer with a Honda civic 1.7D, and previously Astra 1.7D. Both were fine on long trips to Scotland.
The car handbook should state the towing weight limits.
hope that helps