Black smoke is caused by being way too rich, hose coming off the turbo = no boost = not enough air for the fuel going in = no power and loads of smoke.
One thing you forgot is the large brown stains on four seats because of the noise from the open turbo.
The point I was trying to get across is that the chances of getting the same conditions in just the car may be difficult due to the extra loading and heat caused by towing the caravan. In my case the car had been driven enthusiatically on a number off occasions and we were 150 miles plus into the trip when it blew off.
One thing that has come to mind reading this, we owned a MK1 Astra GTE and it developed the same symtoms as the ones here and I couldn't find anything wrong and either could a mechanic friend. We were looking around the engine bay with the enginine running when he put a hand on the top of the convoluted inlet hose between the air box and the inlet to lean over for a look down the back and this initiated the misfire and splutering. It turned out to be the convoluted hose had split in the bottom of one of the Vs and was only opening up and allowing more air in when the engine was getting enough stick to tilt it on the mountings so to speak like when pulling away at junctions etc.
Moral of the story is don't just look at the hoses get them off and give them a twist to make sure there are no splits.
Steve