Does anyone know of one that fits to the existing roof rails without cross bars needed?

never seen one that would fit that way - you're going to need roof bars mounted to the rails i think, that's how my thule fits.

Thanks Rob, I did think so but would be nice to get it a little lower down than on bars.

See here, the Whispbars are about as low as you are going to get...

 

http://www.briskoda.net/forums/topic/217765-scout-wispbars-and-now-roof-box/

Bit confused as to what is going on with the aerial in that thread? Why's it not the usual fold down type as on my pre-fl? Looks like something my 1990 golf had!

There was a craze not so long back for short stubby aerials, they are more modern and therefore look cooler (apparently)!

 

The stubby aerial from a VW Polo is supposedly a direct threaded fit onto the base of a MkII Octavia, and for the purpose of the thread above prevents the roofbox from fouling the longer factory standard aerial without having to unscrew it and lay it flat on the roof.

the polo-sized aerial was oem fit on my 2012 vRS but would still have been too tall and would have conflicted with the box - i have a "stubby" that fits perfectly and has sufficient clearance.