Custom sub box

Hi...

A couple of questions:

1st: i have a Audiobahn AW1000N (700watts RMS) run by a A8000T at 800watts mono. I mostly listen hard rock (Zeppelin, Metallica,...) so i need a good punch. The sub's specs recommend either a ported box of 1.5 cu ft (with a 3"x8" port) or a sealed box between .25 cu ft and .75 cu ft. Which should i use? And if a sealed box, do i go in the middle with .5 cu ft?

2st: for the sealed box, i am trying to design a stealth box so i can keep the trunk space. My question is, does the shape of the box affect the performance. Let me explain. I would like to build a box that would have an rectangular upper section of about 30"L x 13"W x 3"H with a lower, cylinder shaped section of 13"D x 8"H.  I am wondering if the air space in the rectangular section will be used properly by the sub...

Let me know...