Not much space. Plus you would have the wires that would prevent you from taking the doors off in warm weather, unless you wanted to add a disconnect. I would also be concerned about causing a rattle. They make speakers to fit in the foot well that may be easier to facilitate the sound quality you desire.
I would put them behind the dash, as trail rated pointed out, you wouldn't be able to take the doors off unless you had a disconnect, then you wouldn't have speakers.