We rarely use interstates and even with our 40' motorhome and towed vehicle we don't have problems finding fuel. Farmers, ranchers and folks that live in the areas need fuel, too. So it's available. Many folks travel to Alaska each summer and if you want remote..you'll find it there. However, I would guess very fuel run out of fuel. You need to plan ahead.
Always run on your top 1/2 so you have some leeway with finding the next station. If you stay in a campground near a town of any size, drive your tow vehicle separately into town to get fuel then you're ready to take off in the morning. It can be done and the secondary roads are so much more enjoyable!