Tow Pro: What is the law - carrying petrol?

I have been seeking a definitive legal view on carrying petrol in jerry cans on a caravan or camper trailer. You often see petrol being carried in jerry cans (plastic or otherwise) on the a-frame or rear bar and even at times on the roof rack of the tow vehicle. Common sense should dictate thar carrying petrol in a container of any sort on the rear bar of a caravan is dangerous if not illegal however the legal situation re. carrying petrol varies from state to state. Petrol is classed as 'dangereous goods' and in Victoria, I think it is covered by the Road Transport ( Dangerous Goods) Regulations however there is no real measure as to how much can be carried. Diesel is exempt as it is not classed as 'dangerous goods'. I would welcome your views.

John Wall, VIC