The road handling of the Sorento is actually pretty good. But all SUV's, including the Sorie, are more likely to roll than a "normal" passenger car because of their high center of gravitation. The sticker on the sunvisor is just a warning, that is probably mandatory by law.
Also, your 2008 may be equiped with ESC (Electronic Stability Control). All the US models have it, but I'm not sure about the rest of the world. If you have ESC, it will be even more difficult to roll the car.
You should have no problems at all towing that caravan. Kia specs 3500kg as towing capacity for the 2.5 CRDi. That means you can almost buy a 2nd caravan and tow both of them at the same time
