I have the support mounted on the Tiguan which went pretty smoothly. But then came the problem. The U-profile my Kamei box (50mm) are 2-3 mm too narrow to get them on the profile (48mm). The included T-slot adapter are much too short, they need to be at least twice as long. The next problem, manufacturers such as Kamei, Thule, Atera go all out, including at least 20 mm T-slot width. Their adapter so all do not fit. Improvise now is announced.
Addition: Bin has shared with Amazon. The Brio rail carrier is identical to Unitec. And for the Brio, there are T-slot adapter 40mm long and 14x14 head dimensions.