Extending a port outside of the box

Okay, so my brother wants me to build his box for him in his 86 MR2..he wants the sub up front, and the only way i could see doing this is to extend the port outside of the box through what is normally the firewall into the passenger compartment.

i am not sure about lengths yet as i havent got into measure it up yet..i am just trying to figure out the best way to port it, so he can hear it in the car.

so my question is,

1>how do i calculate the length of the port if it extends out of the box?

1a>does it even matter? now i realize the port's thickness would normally be subtracted from the volume of the box for more accurate numbers.

2>now if i need a port say 15 or so inches long, is it going to make any difference if only 3" is inside the box and the rest is outside of the box?

3>will i have to include the volume of the port outside the box in the volume of the box calculations, when i go to build the box?

thanx for your time and help guys.

1) same as always, it doesn't matter.

1a) yes, you still have to account for any material inside the enclosure.

2) no, that's fine.

3) no, only the portion that actually takes up space inside the enclosure.

Now here's my question: if I understand you correctly, you are building a system ported into the cabin, but the speaker is still outside the cabin?  The only type of system where this MIGHT work properly is band-passed.  Are you building a band-passed system?  If you are building a standard ported system, then you want the port and the speaker in the same air space, not separated by a firewall.  What's the vehicle?

If the port is going to be outside the box. 

- Don't subtract the length from the box volume, Unless you have "3 inches " inside, then you will have to subtract the volume of the port inside the box from the box volume

Dyohn, beat me to it, I didn't think it took me that long to type that.

yeah i wasnt too sure about putting it up front and hearing it as though it where in a typical truck..

thanx for the input though guys..