Yes, it clamps on the rain gutters! I wanted the kammback to be easily removable without leaving traces of it on the car and still be able to use the trunk. So this was (in my opinion) the best solution I could come up with.
I'm not sure if the photo is detailed enough. I used the clamps and protective rubbers (haha
) of a original roofrack (the black triangles) and took some 3 mm steel plate to attach the aluminium bar to. Pretty simple actually.
The tail/kammback is a separate trunk, I just lift it by hand and then open the original trunk. I later found out that the bar across could be used to support the tail on the trunk while opened.