Also, don't worry about aiming the subs in any particular direction. Just make sure you tighten everything up in the doors and door panels, maybe get some type of spray on adhesive so that everything is sealed nice and tightly with no more rattling.
Excellent idea by the way, i almost attempted this before i bought my infinity kappa perfect 10.1'*
Bass up front is the best way to go when you want SQ, and Jeep does an excellent job at this by putting Infinity 6x9'* in their front doors. That is going to be my next project if i don't sell my car which i am most probably doing.