I got mine from Armitage Trailers at Ferrybridge Rob.
It was a seriously substantial piece of kit and whilst they said it was portable and could be put in the boot of the car when not in use and folded you needed Geoff Capes ( R.I.P. ) to help you get it in there
They also replaced the front cross member of the car with their own that housed the threaded units which held the rings, a Bowden cable worked the braking system. The original front cross member is returned to you so if the A-frame is removed the car can be returned to normal.
I used it for 3 years all over the UK including the proper back then single track roads in the highlands with no problems at all.
We once had the police follow us into a layby who asked politely if they could have a look at it because one of their mates was thinking about one.
What was intended to be a quick brew stop turned into a 2 hour marathon as they were fascinated by it and had a couple of brews with us and something to eat.
We saw them again a week later and it was quite funny as they pipped their horn and waved when they drove past us.