http://www.rms.nsw.gov.au/roads/safe...es/towing.html

Check this out first. I know people are doing this but you need to look at rules. You are only allowed 1.5 times the weight of your tow car if you don't have the manufacturer rated specs. Plus you will need s brake controller.
It's great that it's possible to tow a van behind a van. But the RMS don't give a rats if your overloaded. They are blitzing caravan owners at the moment. I know one bloke who bought a new caravan but they wouldn't let him take it out of the yard because his car wasn't rated to tow it.
I don't know any figures, but assuming a trailer weighs 800kg and a V8 van weighs 1450 (without being decked out with 150kg of plywood and trim in the back) then you are 50kg overloaded. That's without a driver in the tow car as well.