it will work fine... BUT

the driver MUST be in an enclosure to seperate the front sound wave from the wave coming off the back of the cone.
Otherwise you'll have almost no midbass output since they'll just cancel.
The enclosures can be very small though since they won't be playing that deep.
You'll probably have much better performing drivers than in your door... better seal and less things to shake/resonate.

Aiming/placement wont matter much if not crossedover too high on it's upper frequency...