As someone who frequently drives ~600miles/8-10hr trips across my province, as well as 2hrs to and from work each day, I wish there was at least 30gal/120L tank option. Time is money. I would sacrifice 3-4" of the bed for a clean slip tank install, or maybe even the dead space around the one(or both) sides of the wheel well. That's probably all the volume that's required to make the truck reach my points of destination.
I like the flo n go idea as a backup but I hate the idea of unsecured fuel in the bed, in plastic containers, with poor ventilation.