I just removed my factory cross bars as it looks like the skiing season is over. They where no problem to install especially with the enclosed screw driver that came with the bars. I use Yakamia Rocket box the same one that I have had for the last ten years. You will find that you will have to drill new holes in the ski box to mount it as the bars are are greater than 5cm.
I did noticede that there was some road noise with the ski box on but closing my moon roof cover got rid of it. The real skiing is in the Canadian Rockies where the snow is dry and deep.