Hi Anders,
I don't have a mirror, but with advancing age my little boat was becoming too much to lift onto the roof of a Scenic. I investigated boat loading systems and the best I could find was the KariTek (
http://www.karitek.co.uk/). However, this was way too expensive for me, even second hand on eBay.
I made my own in the end, with two bits of wood that hook under the roof rack and suspend a roller just aft of the car body. I can then lean the boat on end against the roller, and lift the bottom end to slide the boat along the roof into position. The bits of wood then unhook from the roof rack and store away in the car boot.
I could take some photos next time I'm using it if you wish.
Ian