Question about Fischer Xtreme II

You need suitable crossbars/roof bars for the Dacia, which you first mount on your Dacia roof rails. The shape of these crossbars can be square or rectangular - it doesn't matter... The Quickfix is very flexible!

I can't answer that, but ws fit at least 3.5 cm inside for fastening

I don't use the box myself.
That's why I can't say anything about it.

So the box comes without a carrier.
You need to buy a carrier that fits the Dacia and the box.