Here's a link to a box calculator program if you really want to get detailed about things but you'll need to find the specs to these speaks and find out what enclosures they are designed for.

http://www.lalena.com/Audio/Calculator/Box/

Sub direction....you can always rotate the enclosure prior to bolting/screwing the enclosure to the floor to find what's most pleasing to your ears i.e. firing up, forwards or backwards as well as the particular location. Also consider the distance between the front of sub box and nearest parallel surface it faces. Does it sound better when it's a few inches from, for instance, the hatch/liftgate/can't think of right term or when it's as far front as possible which provides a few feet of space between sub and hatch?

the enclosure you speak of......sounds like a band-pass to me if both are firing into the enclosure. the box these subs came in is a single-reflex band-pass enclosure

Depending on how closely you examined the picture of the following enclosure you may also be speaking of an isobaric enclosure....a quick glance may lead one to believe it's a band-pass but upon closer inspection will notice the 2 subs are bolted together and the 2 speaker cones are firing into one another.