Another way of looking at it is, how many MPG's do you currently get when towing? Based off that, plan your fuel stops accordingly and look/plan ahead as to where they will be and what's avail then. If you ave say 8mpg's x 30 gallons, that should give you a range of 240 miles (leaving some as reserve), so base your stops off 200-250 miles each. Most folks will travel 300-500 miles a day, so it's possible you could also plan an overnight at each fuel stop and just take truck to get gas.