I recently discovered a website to help plan your fuel stops.
Find The Cheapest Truck Stop - TruckMaster Fuel Finder
It's free and works great. I usually only travel 200 miles or so between stops so finding truck stops wasn't an issue. When we had to travel from New Hampshire to Mississippi recently knowing where fuel stops would be really put us at ease.
If you travel more than one tankfull at a time, you may find it helpful as well.