Depends if you after sound quality or just want sound. Speakers project sound. They need to be roughly going towards your ears. Bass is non directional so you can chuck a sub woofer out of the way.
It's a compromise what ever you do. Sadly the best place for sound quality is mounted in the metal in the door. I can understand not wanting them there though.
In the back of a van would be next best. Kick panel works but you will kick them all the time and the sound goes straight at your feet.