How far can you tow prior to fill up?

I have, depending on winds and terrain, on different trips averaged from 6.4 to 14.2 miles per gallon but around 10 is average. I have a 26 gallon tank but try not to go below 1/4 tank or about 20 gallons. So at the worst I have to fuel every 124 miles and that sucks. At the best I fuel each 280 miles. Over all I figure about every 200 miles works out about right to fill one reservoir and empty another. I don't know what kind of trailer you are thinking of but most likely you will need at least a 1/2 ton truck.