trunk sub considerations

Be prepared for major sound deadening! I still haven't got enough in mine. Depending on where you mount the amp, you may find that "venting" the rear seat will produce better results. I'd go in with a hole saw and pull back the carpet and remove some steel.

Put that box right up against the back seat, fasten it down with brackets and aim it towards the rear. Be careful when mounting it as the fuel tank and linkage are right below the strut towers.

By venting the rear do you mean cutting holes in the seat? 

You'll have to expose the rear parcel deck for damping purposes, too.  Look at it and you'll most likely find speaker cutouts that you can use for opening the trunk into the cabin.  If there is a middle one you are good to go.  If there are only the left and right, and you're using those for rear speakers, enclose them in hats so they won't distort too bad with all that pressure coming from the trunk.  In the middle between them is a good place to cut a hole.  Build a "tunnel" from the trunk to the inside of the car, and finish it off with a grill.

Here's how I did my Taurus

I used a piece of flexible air duct and two hats (bottoms cut out and one inverted over the other) to form the tunnel.  That keeps the air pressure from affecting the speakers in the rear deck (not seen; hidden under the carpet...OEM look).  A grill painted to match the interior.  So it looks like it could pass for the OEM subwoofer grille because that cutout is where the OEM sub would have been.  Under 200 watts of subwoofer gets very LOUD in the cabin.