I understand about the Thule Cargo Box now. I didn't realise that it mounted directly into a hitch receiver. I have a Thule towbar mounted bike rack that ratchets up onto a standard 50mm ball. Ironically Thule is a Swedish company that has reworked their Australian products so as not to have a European 13 pin plug, but our 7 pin flat one. Not that it matters, because you need the hitch for the box and the Treg. As DunlopRS said, there are a few threads on towbars, and towbar wiring, which I haven't fully read as I'm happy enough with my set up, but it looks more and more from where I'm sitting that your only option is a HR bar.

It might be worthwhile talking to Steve at Shop1auto, Gladesville, Sydney. They do the HR bars for Skodas, and are a sales agent for Thule. The other guys there are good at what they do, but Steve is the guy to talk to about wiring, and finding a good set up for what you want your towbar and wiring to do.