"Maximum load, distributed over the roof bars, for a loading height not exceeding 40 cm: 80 kg.
This value is subject to change, please check the maximum load stated in the instructions provided with he roof bars. If the height exceeds 40 cm, adapt the speed of the vehicle to the profile of the road to avoid damaging the roof bars and the fixings on the vehicle.
Please refer to national legislation so as to meet the requirements on carrying objects that are longer than the vehicle."
It looks like the rof bars fit under the rails so shouldn't affect the finish.
I bought the roof cross bars just after I got the car but I haven't tried them yet, I got them for 'just in case I needed them' in the future, they were £124.00GBP. I had a quick look at them and they appear to have a rubber type lining to protect the finish of the roof bars, that's all I can tell you i'm afraid.
I've just found a set of Roof bars in B & Q. Made by StreetWize they fit really well with rubber protection for the car's original roof bars and they were priced at £47.00!
I've fitted them to the car and am using it this weekend with them on. There is some wind noise but I think I will be able to reduce that when I alter the position of them.
For occasional use I can put up with a bit of wind noise.