Interesting and great looking tractor.
My dealer/salesman had the literature, and had been to a meeting to test drive and become familiar with the new tractors.
I would just use a funnel to fill the new one with fuel. It helps, as well as it would be okay if the fuel was in a barrel and a hose and nozzle was used instead of a 5 gal container. I don't like the position of the fill for the fuel either, but I suspect this is the least disruptive of the many give and take options and decisions the engineers had to make. I don't see a lot of room behind the seat for a tank, IMO.
(P.S. Kids gave me a shirt for Fathers'Day that says "Friends Don't Let Friends Drive <font color="red"> RED </font> Tractors" followed by a green tractor. Sure received a lot of good comments while walking the streets and shopping today. )