Sealing up the door panels for better sound

When I was mounting my speakers in my front doors, I popped the panel off and the door itself looks like swiss cheese. the 6.5s I had in my old truck used to sound pretty decent going low cause they had a good seal.
The question is: Who's got suggestions for sealing up the door itself behind the panel to clean up the bass? Would dynamat/dynaplate work for this or would it flex too much on larger openings? I could cut some sheet metal to glue in there, but that would be a major PITA and I'd rather avoid it if possible. Tips?

make a fiber glass pod. contour it around your new speaker

I haven't made any pods before but working glass is not beyond my skills. I'm not really familiar with how to design one, they are sealed or do you make them breathe any? When it comes to serious custom stereo stuff, I'm a bit of a n00b.

hrm well make it almost all sealed except for the bottom area.. this will allow you to wire it up an also allow moisture to escape

gotcha. now to I want to make the back larger rather than smaller? or do i want to shape them close to the back of the speaker?

close to the speaker would be best.. just cover one up good in tinfoil n tap n hope for the best