Gas tankers supply gas stations. Gas tankers are longer than anything that we RVers drive.
We don't try to do truck stops only. Better prices are usually less than a 1/4 mile further from the exit. For us almost every station has diesel. Almost every station has diesel/gas pumps at the end of the line of lanes.
The biggest issue is often the thoughtless car driver who uses that end pump, blocking the use of the diesel pump, & has gone inside for food or bathroom & has abandoned the car instead of moving it or using a gas only lane.