We mostly travel up and down the East Coast, and generally prefer the Flying J's to the Pilot's as they are more likely to have an RV lane or two. Since we have a relatively small diesel tank, we prefer the smaller nozzle as the higher flow large diameter hoses need to be held in place for us. The RV lanes have both, and large diameter ones on both sides like the truck lanes.
But to answer your question, if there are not RV lanes, there are usually at least a couple (but not all) of the truck lines that have the regular "pay at the pump" machine that the car and RV lanes have, in which you just scan your RV Plus card, put in your PIN number, and pump. In most of the other truck lanes, you have to go inside to leave your card and pay.
Hope that helps ......