Yes it does look wierd, but, and there is a but, they can carry up to 250ltrs of a fuel / diesel, providing it is outside a confined compartment...the method of carriage is debatable, plastic jerry cans...not too smart.
There is different amounts of diesel carried compared to ULP, this depends on the state you are driving though. In NSW, ULP, you can not carry in the pictured representation, but if it is diesel, name your amount, providing it is a proper carrying cannister, again debatable in the state you are driving through...typical....