"guess that answers that question, next stupid one, is it a case of changing the radio antenna, or is there wiring and "stuff" involved ?"
NO the sets are normally supplied with the GPS antenna and you can put that anywhere you like as long as it is not obscured by steel - plastic and glass is OK so you can mount it under / on your dash.
All other conections are simply the same as any standars VW set and you use your original radio antenna!
