On my car, I removed a foam block in each door and installed the crossovers there. You can cut holes in the plastic covers and flush mount the tweeters in them. The position is good for sound quality and they look like they were made for the car. The woofers need four screw holes drilled in the door.
At moderate sound levels, the stock head unit sounds fine after loudness and EQ are defeated. At higher levels, the speakers will sound better driven by an amplifier.