My solution to the inside corner dilemma was pretty simple and it did come out really nice. I overlapped the "tabs" on the panels and just cut them short so I could push them into the corner without any gaps. I had to trial fit a LOT of panels to get 10 matching pairs, but nothing a little patience, time and a Sharpie marker didn't fix.

Normally I stagger rows to keep the panel "seams" from being so visible, but with the outlet cutouts, I decided I'd get the first two rows done and then worry about staggering everything.