not knowing what the doors are really like, it's a bit hard to provide heaps of advice.
as mentioned, if new pods, locating the woofer at the bottom-front of the door can be made/used, then consider that. otherwise, make do: if space behind the stock trim allows, then build an angled mdf mount, even if it's 10~20 degrees. cut 2 rings of mdf, and join them on an angle using mdf spacer-blocks to support the gap; i filled the space between the mdf with expanding foam (judicious amounts) and it worked a treat.
if there's no room, and you are limited to the stock location, then instead concentrate on sound deadning the doors, sealing them, and at least mount the woofers on an mdf ring which is more solid, and doesn't resonate, compared with either plastic or metal.
what's the stock tweeter location? ideally mount them in the kickpanel region or down infront and below the woofers. although taking the time to experiment with different locations (eg: have the tweets temporarily wired with long lengths of wire, and use blu-tac) and angling to find the best position would be worthwhile.
good luck

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