1) The lower the port tuning, the lower the freq. the sub will hit. The high end is determined by the x-over freq.
2) Fiberglass in a spare tire well will prevent the metal from flexing and resonating. (I used 2 layers in mine)
3) Dont' really know about box explainations...web sites I guess. I don't know of any off hand.
4) I get my carpeting/fabric from the local fabric shop. If there is minimal chances of stuff hitting the box, it works great, and you can pick anything you like. If there is a big chance of things hitting the box then I would go with automotive carpet that is commonly used. Ask at auto and car audio stores.
2006 Jeep Liberty
Adire Audio, Cadence, Clarion, MB Quart
Lv = [(14630000 x R^2) / (Fb^2 x Vb)] - 1.463R
*Vb = vol. in cu"
**R = sq.rt. A / Pi (for square/slot port)