I used some RF 8" in the doors. They are deeper than stock. But I removed the magnet covers, then used a heat gun on the inside of the chamber where the speaker sits. Using the gun, I heated the chamber up and while still hot pushed the speakers in to "mold" the shape. I did this several times and the spaeker literally fits like a glove. There were a couple of holes left from the original set so I used some ABS plastic scraps and some adhesive to plug those holes.
That looks really good! did you notice any increased rattling? I was thinking of doing the same but wasn't sure about sound deadning and if it's needed.