We use gasbuddy.com when doing our route planning so we can easily make it from one fuel stop to the next to get diesel. More than half the towns we pass through in the Western USA do not sell diesel. The truck stops like Flying J and Loves are the best in general though we do have one that is currently a Valdero in our area that has truck bays and a special lane for RV's. Mavericks in the west also has good prices and large fuel areas.
We will fillup earlier than necessary to avoid dealing with small gas stations in small towns that are usually very difficult to get into and impossible to get into if there are lots of cars at the pumps. In mid-morning it is easier to find the pumps vacant and not have to deal with vehicles and brain dead drivers. I have been at pumps many times and had vehicles pull up in front of me to wait for me to finish at the pump with their German cars with the fill cap on the passenger side and there was nowhere for me to go.
Truck stops as mentioned are your best bet. Easier to get in and out and they have much higher flow rates at their pumps. Takes a fraction of the time to fillup.
On a side note if I was buying a pickup for towing a trailer I would definitely get a long bed. The fuel capacity is usually higher from the factory and the aftermarket tanks from Titan and Aero Tanks are more common and larger as well than those for short bed trucks. Having a 60 gallon or more fuel tank is great for diesels.