I think your swinging more for range anxiety. I would just like to have an accurate fuel gauge. The rotopax would be good if I was in a very remote location or taking a long journey, but, that's 30 extra pounds on the back and you've lost the paniers. That means stacking things high on the pillion, which I personally think is bad for CG. If I had to get an extra 50 miles of range, I'd probably just carry a couple MSR bottles. There's a couple luggage manufactures that make MSR holders, like Mosko Moto (just got their Back Country 30L duffle and it's amazing quality).
Not trashing this mod. Just think if you need a 200 mile adventure bike, this is the wrong pick. It's not designed to carry 50 extra lbs on the tail. It's a little hooligan bike that got some touring mods.
I swear there was a extra large fuel tank that somebody was designing many years ago. I think they had a product for the air cooled Hyper. They enlarged the lobes that draped in front of your knee caps, which actually probably helped block wind/rain from your lower body. This is where you would want the extra weight ideally.