Diesel fuel is blended by the fuel farm, in the summer it is untreated #2 because it needs no anti-gel features, in the winter it's #2 with anti-gel properties, some places don't winterize until the first cold snap.
Put in fuel treatment (lots of argument here on it) every third tank fill-up, or just before you are going to sit for 3 weeks or longer, this is true especially in very cold or very warm climates. Fuel will gel at 32 F if not treated, and algae will grow in the summer time because of the humidity and heat. Only buy from places that pump a lot of fuel. Yes, generally truck stops are higher priced, but they pump thousands of gallons of fuel every day, and have drops twice or maybe three times a day to keep their tanks full. Not saying you cannot get a bad load of fuel but saying a "inch of prevention is worth a pound of cure" is my way of thinking. The fuel conditioner is around 8 - 9 dollars a quart, and it does a good job of keeping the algae out and the fuel from gelling. I have never had a fuel problem period, and that is the way I manage the diesel engines I have owned since the late 80's. Got a bad load of fuel one time in CA, and just drained the water/fuel separator and that fixed that issue. It was a contract Flying J station, marked it on the map and never went back to that one.
I have driven this year from Vancouver, WA to Atlanta, GA and almost back and living by that rule above have never had a problem with fuel. I had low temps in ATL to 7F and the diesel burner ran like a clock doing a reasonable job keeping the coach warm. Or you can experiment and have issues, your choice.
Monty & Janet - 2007 Alpine APEX 40 MDTS
S/N - 75715 - Retired - Master Certified RV Tech