How tall is your typical trailer?

Mine's 11' 1" with the A/C.

It really depends on the brand, and more so the model. Within Jayco's offerings for example heights can vary by 6-8 inches. And most manufacturer web sites list heights that include the AC, because clearance is more important to most buyers.

If you're calculating for mileage, I think we can save you the trouble. There is generally not much difference in mileage no matter what you tow. Weight is more of a factor than frontal area. Mileage can range from 8-12 depending on trailer weight and vehicle configuration.