I would suggest contacting Phil Taylor Towbars on 02392594675. I went with them on the recommendation of many other Briskodians, and they were absolutely superb! I had a PCT towbar installed on my Yeti, based on their expert recommendation. They have a panel cutter, and can make the precise bottom panel cutout, with fitted lid insert, that would normally be made by the dealer. (No other aftermarket installer I've seen offered this option.) They do the standard Westfalia towbars that come stock from the dealer, but can recommend other options as well, depending on your model vehicle. I was looking for a removable towbar with the maximum possible nose weight, to mount a bike carrier. Your mission may vary.
Best of luck!