Although the doors are not completely sealed as is from the factory, and these speakers (size) are really not competition ready, you may end up reducing the bass from them even more by creating a non-mated surface to the door. Unless you design a mount that is flush to the door and the speaker at an angle you will not be flush.
Polyfill will do nothing and I can speak from experience. A little bit here and there is a waste of time. Seal it, Mat it, make a flush mount....... You can do it.
2013 5.0 STX - Coyote Blanca
Harley Heads/Tails, Alpine KTP-445u, Infinity Kappas, Rugged Liners, 20% Tint, "Coyote" Badges, JLT Catch and Tremor Grill.
Last edited by O.C.D.; 11-05-2013 at 10:00 AM.