Does anyone use a roofbox and cycle carriers on the roof of their car? I have 2 Thule 591 cycle carriers on the top on my Passat estate with 120cm Thule bars. Is there a box narrow enough to fit alongside the carriers?

yup, no problem

Any clue as to a model?

I have a Thule box (one of the narrowest), and 3 carriers – 2 x 591s and the one with the fork mount. It just fits on the aero bars.

Aye, no problem. I use two Atera Giro AF bike carriers together with a very old Jetbag box which is the same shape as this one.

Yes you can. I have a Thule Pacific 500 box, and can fit that on my roof bars with three bike carriers. It is a bit of a squeeze but does fit. That is on a Passat Estate, I am pretty sure mine are the 120cm Thule aero bars.