Funny story. I purchased my Duramax and it has 60 gallon tank in the bed (maybe really 40 + 24 factory). Anyway, my old hauler was a '99 Chevy 2500. When towing with '99 we'd go 125 miles and have to fill it. The diesel goes much further, even at 10mpg towing, I can perhaps make conservatively 650 - 750 miles.
I had filled the truck to the max months before the virus. But my campout was rained out. Then virus came and I must've gone 18 months on that tank.
The Duramax isn't my daily driver, or even my 3rd vehicle to drive. But when raining, I'd take it out.