Thanks for your comments guys/gals
I doesn't really clip to the gutter. It fits around the gutter and under the door windows - around the frame.
I intend to do regular biking, and took two mountain bikes out the other day, it was very stable and didn't cause any marking.
It is designed to carry up to 50kg, my bikes are quite light though!
Although I really got it for my 7'10 MiniMal surfboard
Might also consider a box for camping .....
It's no probs with sunroof
the sales pic has one. The feet fit quite close to the edge.