very easy to make a door pod for that door.
first, cut a piece of 1/4 MDF to fit over the shape of the small holes on the door panel. mount a couple 2x4's or something of that nature on the back for support.
Then, cut out a ring for your speaker, and if your using components, also cut a small ring for the tweeter. Round the outside edges with a router. Mount the rings for the speaker and tweeter on the board that goes on the door using small sticks of wood, and a nail gun or glue at the angle that you want them to be.

After your happy with the direction that your speaker will be pointing, stretch cloth tightly over the front and staple it on the back, hot glue will also work, but won't hold as well as staples.
After the fabric is stetched, use fiberglass resin, and soak the cloth, this will give you a nice smooth shape. After first coat of resin is dry, then you can start fiber glassing a couple layers one the pod, don't use bondo glass, it's not very stong, use fiber glass and resin. When figerglassing the pod, try to glass the inside as much as you can, it'll save you alot of sanding in the end. Once you glass a couple layers on the pod, and it is good and strong, use a quility bondo and bondo the outside of the pod, sand smooth, repeat if needed. When glassing is finished you can remove the 2x4's, or whatever you used, replace the pieces you cut out, glass the cut out pieces on booth sides for strenght. Once you are satisfied with the surface, spray with scratch fill primer. You can accually get it in a can at Canadian Tire, then paint. or if your not painting the pods, vynle them.
hope this makes sense, keep asking questions if you need help.