The roof box was also something laying in my garage, unused.
I had sereval bars from different cars. I used 127 cm long bars, came from a Volvo S80, 15 years old. Normally they can be 10 cm shorter, but they fit, I can even put 2 bikes along the box. I only bought new feet.
Even now, with the bars on the roof, no wind noise.
The box is great to put some not daily used stuff in: inflateble boat, extra chairs, tent for the kids, toys,...
The only thing is that I have to take the things out that you will need, before I attach the tarp, otherwise you can't reach it anymore.