Bridgid as mentioned above by Benkie, the engin strength dose play a role, but to stay legal you will not be able to tow anything exceeding 750kg. This is where DK's post come in about a smallish caravan. Hope you get sorted out.
I think some correct and some incorrect comments above. Due to out of warranty if another engine that is strong enough is put in you can legally tow up to 1080kg(tare of Corsa) if the specs are right for a caravan with run-in brakes. You can confirm the tare of the bakkie on the licensing disk.
The second point will be the manufacturer gave a maximum weight you can tow as 670kg. This follows that insurance can come into play if you exceed the 670kg. One will have to find out what their conditions are with such a modification. This mod is then just to get more power/torque to pull as small caravan.
Interesting it seems like a Corsa light car with the same engine as the pick up pulls a lot better.
Hi DK. We have given out opinion about using a Corsa. I also mentioned the fact that the Corsa Lite with 1400 engine and Pick up I drove recently were like cheese and chalk as far as power is concerned. I tried to indicate what is legal. Due to the tare of the bakkie it would be legal to tow 1080kg. I would never even try to haul any of the vans you indicated with the Corsa 1400pick up. A Nissan 1400 would tow much easier but the weight of about 700kg is just too low to be legal. Yes if it was other 1400cc cars it might be OK like the Golf you indicated.
This is just like a magazine that indicated one should look for nothing smaller than a 2.8L TDi while a lot of 2.0 TDi would be just as good for towing a specific weight.