Well, I managed to get all the airtabs installed while I was in TX. 5 on the roof, and 8 down each side. Using the spacing that they recommend, 8 on each side fits just about perfectly - bottom tab is right at the top of the rear fender flare.
The way the rear pillars are curved, if you have the front part of the tab flat, there's almost an 1/8" gap between the rear pointed end and the vehicle. I used two layers of 1/2" wide double-sided foam mounting tape under the very end, the width of the tape, to anchor the end and give it some support, and this still allowed the front scoop to be seated firmly without any gaps. The lower two in front of the taillights only required one piece of tape as the body panel had less curve to it.
Hard to quantify what difference it might have made, given the drastic difference in weather between the journey down and the return. Until I blocked off my fuel cooler and aux tranny cooler halfway home in Arkansas, bloody thing probably wasn't even getting 20 MPG due to the cold temps.
However, once I did that, it gave every indication of at least pushing 30 mpg given it's performance on the last 1 3/8 tanks of fuel - 180 miles on 3/8 tank, and 500 miles down to 1/8 tank on the final leg home. On the last tank while it was still daylight and temps at least in the low 30's and before I got into the TN/NC mountains, it had hit 250 miles by the time it was down to 3/4 tank. That's almost equal to it's best performance back in May with temps up in the 80's and 90's. Not too bad for winter blend Shell Diesel, sub freezing temps, and wider than stock 245/70 tires.
The 4 grill blockers definitely helped, and as cold as it was, I probably could have blocked off the whole bloody grille and still ran 70 mph without any problems. Coasting down the 6 mile long grade at Black Mountain near Asheville NC, I watched the temp gauge go from just under 1/2 down to 1/4 scale.
Rear window did stay quite clean for most of the way across - only a light coating of road dirt. Best I could tell after I had the coolers blocked off and getting decent MPG again, on what fairly level ground I came across and when the Scangauge was working, the airtabs looked to be decreasing fuel flow by at least 0.2 GPH at 65 to 70 mph - from 2.4 down to 2.2 GPH.
I also tried drafting some OTR trucks at various times, usually about 4 to 6 car lengths back, never so close to where I couldn't see their side mirrors (and they couldn't see me behind them). On average, this knocked fuel flow down by 0.5 GPH by the Scangauge. There were times on level ground and at just the right distance that the Scangauge was showing 1.8 GPH at 70 mph - that's well over 35 MPG.
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