more accurate, louder

• "This creates a bass- reflex type effect."

Where is the Helmholtz resonator?

• "Now as for tuning- your on your own!"

Tuning what?  It's a sealed enclosure.  There's no resonator.

It's a sealed enclosure... downfiring.  Period.  You just got a different response in your application than what you had before.  Experimenting with firing direction is a good idea in any vehicle; but before using a downfiring direction, consult a sag calculator to be sure that there are no long-term negative consequences resulting from having the driver in this position.

Interesting:  historical note found in http://www.diracdelta.co.uk/science/source/h/e/helmholtz%20resonator/source.html

"The Romans used helmholtz resonators formed from clay urns to tune the acoustic characteristics of ampitheatres."

http://en.wikipedia.org/wiki/Helmholtz_resonance

blackmica3, the driver is damped by a sealed enclosure and is providing sound through the driver only.  There is no additional resonance and output source as there is with either round or slot porting.  Confining the square inches of airspace in front of the driver doesn't equate with adding a resonator.

jmelton86, best results are most often found by firing toward the rear of the vehicle, and actually fairly close to the rear.  But every situation, system and car is different...so if you can move the sub(s) in different directions and test with a SPL meter you can find the most output.  Finding best quality sound is easier...you only have to sit in the driver's seat and listen.

The port, whether it's a plastic or PVC round or whether it's MDF slotted, is a resonator.  The principle of "tuning an enclosure" by manipulation of air mass and neck opening (diameter) of a port is derived from the discoveries of Helmholtz (who you can read about in the Google search).

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.