I know this is not exactly what you are asking but here's what I do and it may help you.
I have a 40 gallon diesel aux tank in my bed, that gives me a total of 78 gallons onboard. I generally do not stop for fuel during the day but go get fuel either after I've set up in a campground in the evening or in the morning before I leave. I use gas buddy to find fuel. This way I can use the 'normal' stations if they are around. Many times I need to get groceries, or grab pizza etc anyway so I just combine everything into one trip. This works well most of the time.
Tim