forget about the weight and capacity and COG issues for a minute..... at 565mm high it's gonna sit a long way above your vehicle for a start, get a tape measure out and stick it up above the roof of your vehicle to get an idea what i'm talking about. the wind drag issue aswell as the COG issue and then the weight of it all shows it's probaly not a great option IMHO. even if you were to fill it with only 60ltrs to help keep the weight down, the empty weight is nearly 40kgs...that's like having a couple of bags of concrete on your roofrack all the time and then you'll add another couple more up there when you add the 60 ltrs of fuel into it to be the same as 3 jerry cans (hence the COG comments people are talking about). personally i'd stick with carting 3 empty jerry cans and just fill them as you need them, you'd save money in the long run even it means paying a touch extra for the fuel as you buy it out wherever....quickly empty the jerry cans as soon as possible into the vehicle and you're left with minimal weight to carry after that.
a mate took something similar across the Simpson Desert when we crossed it a few years back, but he had a ute and it was a different shape to that and packed away perfectly in the back of his set up, not up high on a roof. I have a 180ltr longrange tank in the back of my cruiser....i certainly feel the differance straight away in handling characteristics of my vehicle when it gets filled for a big run somewhere, i'd hate to try and have that weight up high instead of down low in my vehicle