Setup: Alpine CDE-HD137BT head unit, MB Quart ONX4.80/500 Amp (5 channel amp @ 60 watts per channel RMS @4ohms, and sub channel @ 250 watts @4hohms), sub is a Boston Acoustics G112PS 12 inch sub handling 200 watts RMS @4 ohms. The midwoofer/tweets are JL C2-650 and 650x

This is going into a 1996 Saturn SC2 coupe. This OEM speaker location are fronts on the doors and the rears are behind the back seat over the trunk. Sub is in the trunk.

Here is my basic question. (I know that the sub is not going to put out tremendous bass, but I am going for simplicity and bass to fill in the balance.) Is the sub going to compete and cancel the mid woofer effect on the trunk ceiling? The sub will be pushing SPL inside the trunk and pushing against the back side of the midwoofer cones, and if pushed hard wouldn't that prevent the midwoofer from performing?

I also noted from past experience with this car (I had a small infinity self-amplified sub) that it would sound better when my back seat would open into the car.

So here is my thought. I could build a very shallow box to contain both midwoofers (JL-C2 650x) that would sit in the back over the trunk area. I would also leave the 2 holes where the OEM speaker cut outs are to be open to allow the new sub to effectively be open in the car.

1. If anyone recommends this box to be built, what materials to build out of and how much volume would need to be included. I am assuming 3/4 mdf, but the volume wouldn't seem to be such an issue as it originally had trunk space (huge), and can fit in the small volume of a car door. I'm just thinking of needing to separate the air spaces from the sub.

2. If volume is an issue, would you need to tune it to what the midwoofer is capable of doing? It can go down to 50 Hz.

3. Would another speaker location be better, like having 2 sets in the doors (one component and one coax) or next to the armrests in the back seats? The problem here is I don't know if they can fit without serious modification.

4. If another location is recommended, should I leave the 2 holes in the trunk stage for the sub to fill the car (OEM grills still cover so you can't see the holes).

5. Am I making this too complicated with such a simple system and just put the coax in the back and forget about it. If that is the recommendation, should I cut a hole in the trunk stage for the sub to fill the car, or any other suggestion?

Ok, be nice as I am new to this.