Dynamat

Will putting dynamat behind the speaker help anything, and i dont mean where it screws into the sheet metal, i mean in the actual housing where the magnet is.

Debatable, but in theory, yes. This piece of sheet metal resonates just like the sheet metal the driver is attached to. This resonance can reduce the bass energy. Dynamat can also help break up the backwave from the driver.

https://www.cascadeaudio.com/prod/deflex.html

These pads work substantially better than a little piece of dynamat.

I layered both walls of sheet metal in my doors with multiple layers of raamaudio mat. Then placed cascade deflex pads behind the drivers. Did it help? Yes. Not only did it help kill some road noise, but midbass is about as tight as I can expect from my drivers in that door location without physical door mods.

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New Project: 2003 Pathfinder

I did what kfr01 did, used damping on both the panel and the outer skin of the doors.  Makes the door a bit heavier but feels solid, thuds when you shut it with no metallic ringing.  The improvement in bass response is amazing.  As far as the deflex pads go, I used Dynamat's version but the jury is still out on whether they make any difference.  My ears don't detect any, and I judge it by putting the window up and down and trying to hear a difference.  And there is enough natural curving in the outer skin sheet metal, anyway, that the waves shouldn't reflect directly back into the speaker cone.  They'll most likely break up and spread into the door's interior.