Should you travel with a full tank of Gas?

Gas motorhomes have an 80-gallon fuel tank. Since you would be a fool to have less than 1/4 tank, that means the difference between a full tank and a low tank is 60 gallons. If I remember right, gas is about 6 pounds per gallon, so we are talking about 360 pounds. If you have a 20,000 pound motorhome,a full tank would be about 1.5% of total weight. So you could get 1.5% better mileage, right? Oh wait, like Wolfe10 correctly said, mileage difference due to weight is really only a factor when you go uphill, so you would have to multiply that 1.5% by the percentage you go uphill. If worst case you go uphill 50% of the time (doubtful), you would have a 0.75% difference in mileage--which of course would decrease as you use the gas in the tank. I think your time would be better spent making sure your tire inflation is correct, and going easy on the throttle!