Sean, a bit late with this, only just seen your posting.
I have had several cars during my caravan years, the main problem I found is that most car dealers do not understand caravans. Always had problems with the fridge supply not working whilst towing.
I am talking about fairly recent vans (last 10 years or so) when 13 pin electrics replaced the old twin 7 pin plugs, the 'S' and 'N' if I remember correctly
So, a bit late with advice but the problem is not with the tow bar (which all have to be type approved) but the electrics, modern cars are so complex that I would not attempt to fit my own.
Long gone are the days when you could knock up a tow bar from angle iron and drill holes through the boot floor, scotch lock some wiring and away you go.
Bill D.