Might be hard to build an enclosure in the door, so I don't know if it will be worth it. But it would sound better if it's a two-way system. You can line the enclosure walls with open cell foam or some other soft material to catch reflections from the back of the speaker cone which can color the sound - that's hard to do in the door without an enclosure. Plus, the speaker is better protected from the elements. Better yet, if you are willing to go to all that trouble, I would recommend an enclosure in the kick panels - it's an even better location than the doors.