The GasBuddy app has been mentioned and it's one that I have used. You select the type of fuel (gas or diesel) and if you activate your mobile device's location feature the app will show the fuel stops nearby or you can pan down the route to check for stops farther away. There are probably others so you might try them out and select the one that works for you.
2016 Thor Synergy TT24 3.0L
Ed & Robin Lively
with Nina, Kitt, and Mickey
2016 Thor Synergy TT24 (a.k.a "Ming")