Crunching the numbers from this year's trip to Tampa, my best mpg was 26.4mpg coming back home. I'm sure it would've been closer to 27mpg if I didn't have to make the multiple pit stops fer my passengers...
So compared to last year's drive (without rear wheel skirts), the mileage seems to be more consistent and a little better this year. This year's mileage was easily over 25.5mpg while last year's was about 23.5mpg.
2012-13 Tampa trip 2108 miles/82.4 gallons = 25.58mpg
2011-12 Tampa trip 2183 miles/93.3 gallons = 23.40mpg
10.9 gallons less fer the same trip.
By comparison...if I was just gitting 19mpg, I would use about 110.95 gallons fer the 2012-13 trip and 114.89 gallons fer the 2011-12 trip.
Fer the 2012-13 Tampa trip...the difference is 28.55 gallons x $3.20 (estimated average cost per gallon of gas) = $91.36 saved
over stock EPA est highway. Not bad fer just one trip, eh?