You really shouldn't have any issues finding gas. Distances are great in the West so when you hit the halfway mark start looking seriously. Don't wait until you're too low. Keep in mind those gas apps don't include 'all' of the stations.
Full-timed for 16 Years . . .
Traveled 8 yr in a 2004 Newmar Dutch Star 40' Diesel
& 8 yr in a 33' Travel Supreme 5th wheel