Ditto on a handful of replies above:
- Start looking for fuel at 1/2 of a tank, you get to be way pickier than if you're at or under 1/4 of a tank
- Carrying extra fuel is something that I'm going to start doing after a particular empty stretch of highway on my last trip
- Truck stops are your friend- go around back and use the truck lanes
- (If you do use truck stops, be mindful of etiquette - pull forward after you pump to let the next truck into the pump while you go inside and pay)
- Look for the Flying J RV'ers card
- If you're a smart phone user, my wife has used Google Maps to get a satellite view of the upcoming gas stations (and food stops) to determine if we could likely make it or not