Testing shows possible 5% increase in FE with a open-ended kammback on SUV

[elhigh]

"I just built those things with my new welder, it was my first welding project..."

OOPS! Sorry! <facepalm>

Okay, try this: for when you're not loading the roof, fill in the spaces under the rails with solid pieces of built-up coroplast. A bit like rocker panel skirts would go under the car, except this is above. It'll prevent turbulent flow forming downwind of all the uprights except the last one. Pop 'em out and stash them when it's time to go wheeling.

[ECONORAM]

First, nice work. 2nd, what app are you using? Does it work with vehicles that use MAP, and not MAF? Those seem to be harder to find for phones...
3rd, I suggest you cover most of the belly, if not the whole thing with a set of panels. Cut some slots under the engine bay, like sets of louvers, or something to ventilate. This will really help if you go to electric fans. I found if I sealed the engine bay up too well, then it wouldn't vent the air out and the efan acted more like a circular wall instead of a fan. I'm finding since I had to revert to my clutch fan, the highway mpg isn't impacted as much as I feared. The panel kit also keeps the belly cleaner!
4th, you might look to see if you can get an under drive pulley for the crankshaft. Definitely check some forums out to see what units are reliable. I tried bypassing my power steering and a/c before with a short belt, but my golfer's elbow would not tolerate that.
5th, cut some corroplast disks to cover your wheels with. Secure them with 550 cord to the wheel spokes. Worth 5%-7% mpg increase on my RAM. Yes, you need to pull them off every 2,000 miles or so to clean the wheels.