if you put a tweeter on the B-pillar, im going to kick your ass.
you want the tweeters as far away from you, and in front of you to the left and right as possible, but as close to the center of your midbass driver as you can get it.
a tweeter is a very important part of a component set. it produces frequencies that the midbass driver can not.... BUT.. it is just that, a PART of the set. if you move it too far away from the midbass driver, then you are hearing the lower frequencies (like the voices) at a different time, and from a different location than your higher frequencies, thus causing a total loss of a decent sound stage.
just pony up the dough, and have someone build you either a badass set of kickpanels, or enclosures in your doors.