With my short bed Ford, I had just under 30 gallons of diesel. Typically we would stop every 250 miles to refuel and always had plenty left in the tank to not be forced to stop where we did not want to. My replacement truck carries over 50 gallons but I haven't driven it under load to get an accurate range yet.
Typically we don't drive more than 500 miles per day so the Ford required two fill ups per day. This was never an issue on those long 10-hour days but it would have been nice to able to do 400 miles comfortably without having to stop for fuel or worry about coasting in on vapor and sucking up garbage off the bottom of the tank.