A bit of "whittle to fit" doesn't scare me. As a co-worker used to say when I worked on Slot Machines in Nevada, "Beat it to fit, paint it to match, call it a day." I can see that the air door opening just below this filter is smaller than the filter so coverage all the way out to the edges isn't necessary, as long as it doesn't rattle around in there.

I was installing the cabin filter today (never had one before I found this thread), that was easy. I even got to spray some Dakota Vent Refresh right down into the intake fan with the A/C on. I'd been having some sour smells coming from the vents after the A/C had been on and off a few times.