[BRG75]

Reversing in a tight, or confined, space is where your experience really does come into play.

There is no ignominity in uncoupling and man-handling the trailer or caravan, if the manoeuvre is deemed (beforehand) as impossible, or simply too difficult.

Uncoupling once you are in trouble -- let’s be kind and say “I gave it my best shot”

You are correct in that the angle, where the trailer has jack knifed, will be different for different trailers.
However, for any one car / trailer it is a constant.

That makes me wonder if it might be possible to set up a visual line of sight, rather than the chains I originally referred to.

Maybe the corner of a caravan (or a corner marker on a boat or luggage trailer) which lines up with the edge of a piece of tape, stuck vertically on the car’s rear screen, and a third vertical rod, possibly mounted (temporarily) on the driver’s seat headrest.

Sitting facing forwards in the driver’s seat, should be constant enough, to then use the rear view mirror to ascertain that the edge of the caravan does not move beyond the line of the other two markers.

Again, apologies if this has been thought off before.

Regards

Mike