You need to be able to look in your car handbook first & find the max tow weight for the specific model you have. Then post up that max tow weight & you may then receive guidance as to which caravans come within that weight range.
If it's 1.6 petrol auto then I recall that has 900kg max tow weight so you need to be looking at late 1980s/early 1990s small 2 berth caravan such as ABI Maurauder or if you want something more modern then Freedom caravans are around 750kg all up.
i recently traded in my 1.6 petrol manual focus, found it had too work quite hard towing my quickstop. although it managed it sometimes i found it lacking somewhat at any incline and overtaking. and revving right up to 4k at 70mph..
i certainly think a van would be too much for it given the wind ressistance that would occur. the quicktop is relatively light and max wieght of 650kg, but add a car full of passengers and luggage it will be a fair old whack.
the limit is around 900kg for the 1.6 100bhp zetec....
4k at 70mph would the be same whether towing or not though. Petrol engines produce their peak power around that figure and it doesnt hurt them running at those RPM's.
A similar sized diesel engine is more relaxing though.
I had a 2L petrol Mondeo and it towed fine, but the diesel model will do the same journey without changing gear on the steeper inclines.