It all probablly depends on what is termed off road. Off road would generally mean any place that is a non gazetted road, so this infact could include any private property including a suburban back yard or shopping centre car park.
What a lot of manufacturers are refering to their products no as is dirt road capable rather than off road.
I would say by the letter of the law as long as you are on a gazetted road or track you should be safe for insurance unless your policy specifically say "off sealed roads" which can happen and is often in hire car agreements.
If 1 tonne was the case on tracks then nearly all caravans and off road vans would be breaking the law often.

