Outer Limits 4x4 Board

I am looking at putting the Rangie ute I am about to build on straight gas. I have found a very nice tank...but it is big. 300 litres.
I am thinking of putting it across the tray just behind the cab. I would probably mount it on the chassis rails and build the tray around it so only a bit of the top of the tank sticks up through the tray.
But it is 1650mm long and I thnk the tray will only be about 1750 wide (if that) and I was wondering if there are any regs that state the tank hast to be "x" distance from the outside of the vehicle?

Adam, i have seen plenty of utes with large lpg tanks in and under the car and some so damn close to road that a speed hump would hit, i would ring an lpg place it post in the general tech area for a more legal response.

PM viet667