I am looking to make a custom sub box setup for the 'parcel shelf' of my AU ute, couple of questions...

i am thinking of getting 2 of these "http://www.pioneer.com.au/au/products/archive/TS-W258D4/index.html" (i know its most likely overkill, but i like symmetry), the recommended sealed enclosure is 18.4 - 35.9 litres.
q) if i have two subs, do i need to seperate the sub box into 2 seperate sealed sections or can i just make it 1 sealed enclosure with 36.8 - 71.8 litres (double the recommended for 1 sub).

the link that i provided is 4 ohm, though there is a 2 ohm version available. I know its just a matter of getting a different amp, but which one am i better off getting? I will run either an amp for each sub or share 1 amp between the 2 subs, then run another for the front/rear speakers.

sorry if that is seriously confusing... :s
but thanks for any help in advance