Re: new speakers don' fit
I recommend using plywood for baffles anyway. Plywood does not soak up water nearly as easily as MDF does, even if you paint it. Have you ever seen a speaker box that got wet? Lots of black mold and it swells + falls apart. Paint your plywood baffle after you have made all cuts, holes, etc.
Use automotive autobody sealant between the baffle and door. You buy it at automotive stores or even some well stocked grocery stores have it. Use sheet metal screws and screw the baffle to the door. Do your wiring and mount your speakers.....done! Takes about 2 hours and you will have a very solid foundation for your speakers.....which this alone will improve the SQ considerably over mounting into the existing holes.
'65 VW Bus
(2) PG Ti 12's, (2) Aura Sound 8's, (2) SoundStream 6.5 coax, (2) Alpine Type-S 6x9's [rear fill], MBQ DSC1500.1D, RF 501X
'02 BMW 330xi (AWD coupe)
Harman/Kardon 12-speaker System Option - sounds good =)