What vehicle will I need ?

Johno59, there are a couple of numbers you need to check to work this out.

there should be a VIN plate on the caravan. On this plate will be a number with a label called ATM xxxxkg

find out what that is and then go to your Nissan manual and look up "towing" and in there will be the max towing load and max download(ball weight)

The ATM on the caravan will need to be equal or less than the max towing on your vehicle.

If the caravan has electric brakes you will also need a brake controller-highly recommend the tekonsha P3 as it is set and forget(almost)

hope that helps
frank

Morning johno.
To begin with, engine capacity is not the first issue you need to deal with. As stated above, check the plates for the rated capacities, nearly all accidents involving caravans are due to the fact the vehicle does not have enough purchase on the road. The weight of the van under braking causes the whole rig to jack knife or improperly loaded vans (not sufficient weight on the towball) can cause the van to pig root, unfortunately when this happens, most people apply the anchors, rather than accelerate out of it creating more sway.
Many motoring organisations run courses on van towing, well worth the investment. I did 4wd driver training for some years, and always willing to learn more. I understand I didn't answer your question, but believe its better to put the horse before the cart.
Cheers and safe motoring.
Tony F8

Here you go, some info...

http://caravanersforum.com/viewtopic.php?f=2&t=4842