I tow my boat all the time, and it weights about as much as your van. It also sits surprisingly high, so it does cop a bit of wind drag- not as much as a van though!
If you have the 2100kg towbar, then holden provide a hitch leveller as part of the kit. they dont provide it with the 1600 or 1200 kg tow bars, simply because you dont need it for those rated towbars.
I havent done a thing to my car in terms of towing (apart from the towbar of course!!). Some people do things like get gearbox cooling and firmer rear suspension. But then they are also towing something which is right on the limits of the vehicle.
The only mistake I see people with towing, is incorrectly loading your car and trailer/van/boat. If you put everything in your boot, and everything in the front of your trailer, then its gonna sag over your car's rear wheels. If you balance things out, then you should be sweet.
I wont tow my boat over 110km/h, and I usually sit on 100. I also will rarely leave the car in 6th gear, as I have found that 5th is good at highway speeds. Bear in mind that I am towing on a crappy road which does rise and fall heaps (I go through the mountains on the south coast of NSW). When Ive taken the boat on the hume highway, at 110km/h then 6th gear is good. But I am also in a V8, so it handles it easily. My VY V6 only had a 5 speed manual, and its 5th gear seemed ok for towing.
Just watch how you react with your steering wheel. The VE is very accurate with steering movements, and you will get a lot of sway with your caravan if not careful.
I always carry a jerry can of fresh water, some coolant and a mixing container. Probably a good idea as a van will cause more drag than a boat, and if you are towing a van up a hill on a windy hot day, then carrying some spare coolant and water is cheap peace of mind!