[travelin texans]

I'm on the opposite side of this fence!
We traveled full-time for 10+ years totaling 300k+ miles with 2 diesel trucks. The '05 had a 32 gallon tank, the '13 had a 36 gallon, I did not carry any extra fuel in jerry cans & didn't have an auxillary tank. I carried a cross bed tool box full of tools/stuff so no room for an extra tank.
Only once in those years/miles heading north on I-25 in Montana bucking the wind in the middle of nowhere was I wishing I had an extra 5 gallons just as we topped the hill & spotted a truck stop where I put 31 gallons in that '05 32 gallon tank, by the hair of our chinny chin chin!
With that said, typically we traveled 2x2x2, traveled 200 miles, stop by 2pm & stayed 2 days. We could typically travel +/-350 miles per tank on either truck, but was a very rare occasion to travel that far in a day.
Finding cheaper fuel off of the highway wasn't ever an issue once parked & drove into town to check it out. If needed there were always truck stops available that I didn't mind using, easy in/out towing 40' 5th wheels.
If you're towing with a gasser all this means nothing. The last time I checked several years ago there are/were no approved auxillary tanks for gasoline. The Titan replacement tanks may be available for gas?