i can see two locations for custom pods on them doors. one is where the grill is at and the more difficult one is where the carpet is at.
if you chose to place the speaker on the stock grilled location it wont be a difficult install at all,
you'll just need to get your creative side out and come up with a cool design and first of all get familiar with the fiberglass, how it works how to mix it how to make it so it doesn't cure in a second and how to make it thicker how to get it smooth how to, how to how to.
i suggest making a trim using the current grill as a template. then two rings one for mounting one for flush mounting the speakers. make sure you make it big enough to fit the grill that came with the new speakers. then mount the the speaker rings to the trim you made out of the stock grill, you can use hot glue or ca glue to get the rings attached to the trim. possibly in two points so that the rings are at an angle facing to a sweet point in the car.
once you have them two pieces solidly attached to each other. now you can grab some fabric be it the easily accessible cotton t shirt , then ca glue or staple the fabric around the trim and covering the speaker ring at the same time making sure that the fabric is nice and tight around the rings and the trim, now youre ready to lay some resin. just one layer, then once thats cured you can do another layer of resin. then start applying the fiberglass from the back of the fabric till you get enough layers to make it nice and solid then you can add some filler to the front. and sand it smooth. once thats perfect. you can ither paint it or cover it with matching vinyl.