I did this with kicker shallow mount 6.5" subs...I also have a sub in the trunk but wanted more up front. It was a pain in the ass, needed another amp, but it was worth it!
Had to cut them in, used plywood as support then surround with a dynomat material. Bought grilles and painted them to match rest of the interior.
P.S- I've had the door panel inserts re-done...the ones shown were brutal
I'm interested in your lower door panel installation. Do you have any pictures and dimensions for the behind the door support for the 6.5's?
That would be really helpful!