I like this question, I have a tow bar fitted to my 1.6 GT, about 8 years ago I borrowed my friends 1tone braked trailer, fitted it to the Rocco and drove 80 miles to the south coast and then loaded a GTX on the back and attempted to drive back, now odly enough I did get back but handling was a problem, I could not do a hill Start, so had to make sure I never stopped on a hill or slope for that matter, the stopping distance was about 3 times normal and led to some very tight bum cheeks, I never took a photo which is a shame but the car did make it without ill affect, I would suggest 500KG unbraked and upto 800KG braked would be sensible.
make sure your brakes are good, tyres will need to be inflated for towing