Ive seen kick panels, but i hear there hard to do beacuse of the e brake and computer
For the back, ive seen in the rear doors, prolly very easy since theres room there already. Ive seen in the C pillar, but it covered the window, and ive seen it moved around in the rear deck in order to make room for subs
I've mounted tweeters on the front door skins, and in the rear on the pillars. Next thing to think about is where to mount crossovers if any. I mounted the rears to the bottom of the rear deck and mounted the fronts in the door opening w/o a problem. If you wanna check out some install pics check out my sounddomain url
I mounted some expensive tweeters behind the air vents in each corner in addition to the components in the door. I played with phase for a while, and decided it sounded better inverted. It really was impressive how much it brought the soundstage "up" from down lower.