That was before I added more screws to hold it on, but its still a bit of a work in progress.
I used what looked like a piece of rubber skirting board I found at Home Depot, 48" long and pretty much fits directly across the center of the bumper cover (which in my case was already damaged so I didn't feel bad tapping the holes in it), Except when I go much faster than before if I stick to 65-70ish I'm seeing between 37-39.9 mpg now where as before it was struggling to hit 35 when one of the panels was loose for the forward undertray. (I did have to combine this with a tire pressure of 40 psig and increased vigilance, however it does appear to have improved my mileage by 1-5%)