If you look at your rear windows there are two marked arrows at the top. The rear bar slots inbetween the arrows and you just tighten the roof bar up until it grips your car. This is probably what the above message is about, if you tighten them up too much they will crumple your roof but its clear to see what your doing and they dont need fastening that hard. They are very secure when placed correctly. The front one has an extra attachment, it has a clip that fits inside the door ( small hole in middle ).
Roof Bars cost £115, Bike Ski cost £70. Cheaper than tow bar etc i looked at.
I dont like the ones that go on the boot / rear of the car.
Let me know how you get one