The Ascape might do better for another reason not brought up. It has smooth walls. Can you get smooth fiberglass walls with the Taylor? while slightly heavier, the smooth walls will net you better mpg's.
IF you truly want better mpgs, get a tent trailer or popup of some sort from a pull behind stand point. Or an Airstream as mentioned. A member that I have not seen posting in awhile, said an Airstream got the best mpg's, as he was an RV hauler with his Dodge pickup. WORST was a ball mount with aluminum siding. Next best to an Airstream was a smooth walled 5W with no front bedroom slide, slightly sloped roof etc.
On Semi's, Aerodynamics can relate to upwards of 30% plus or minus HP needed to move a load at a given speed. BUT, with this in mind, it will take a LOT of miles to make up the cost for some wind reduction devices.
Marty