Sparhawk,
With all respect there is no way that I would trust my buggy on the roof of my car on an inflatable roof rack even if the manufacturers state it will carry up to 80kg!!!
I have opted for the tow-bar mounted rack as offered by Coastguard Kites
These racks are 100% safe regardless of what speed you travel at and it is real easy to put the buggy on and off.
http://www.coastguard-kites.com/bugrackflexi1.jpg