My 2014 Honda pilot gets about 20MPG, but when I am towing the camp trailer that falls to between 10 and 13MPG. I have seen a couple different values as to the actual fuel tank capacity, in real life I think about 17 gallons is the most it has taken to fill it up.
In a trip across the US, this means I need to stop for fuel about every 120 miles. (in parts of the country it can be very far between gas stations)
Back in the era of mechanical fuel pumps and carburetors, we would add a second fuel tank to pickups and SUV's, there was a valve on the floor, that we turned to switch between fuel tanks.
Searching Google for an auxiliary fuel tank for a 2014 pilot, is not finding me what I want.
Are auxiliary fuel tanks still an option for modern SUVs?