I used Hempel Varnish on my boats, and had no real problems.

I used nylon, and put 2-3 coats of clear varnish on it, and then a coat of coloured varnish.
it looks smooth, and gets a little bit scraped on the keel when I drag it over rocks and such, but I usually just touch it up with a little bit of varnish after 4-5 paddles and I've not had any leaks or such.

www.matthias-kayak.blogspot.com
www.emma-kayak.blogspot.com

Where in sweden do you live? :P