booming

I was thinking something around 41x22x22 with a 6" port giving the port 120 in^2 of area (30ish hz) just over 5.25 after displacement and bracing using 1" "wood"

42 3/4" long x 42" deep x 34" tall

Thanks I'll make sure to have him look to see what it says in the vents. And as far as the t-line, like I mentioned I think he just was surfing around the net for ideas and came across someone saying the seen a gain by going to one so he figured he'd start out with one. I opened his eyes a little bit with some expert help and told him he would be looking at a box the equivalent of a 10 cube ported box and "that a proper t-line design would make it 4-6ft in one direction (normally width) ". I asked someone that builds boxes on regular basis to give me a "visual" example of why it wouldn't fit in his rig. So now the question is with the power he'll have on tap where should we start shooting for ported wise? Spec say 5-8 but that to me seems like a lot of trial and error so I was hoping to get a smaller window to try for (from experiences with the sub and about the same power)

That was my next question is what would be a guess on an over all dimension of the t-line. Again he is a little new to the fun that is car audio so I think he was doing research (like I wish a lot of younger bassheads would do) and I think he just found some info about t-lines and said "let's try this" so I want to reply to his requests with facts not "I think the box would be way too big" with out numbers or proven alternatives!

So I'm new to this forum, but hoped I could get a little bit of help on an upcoming build I'll be helping a friend out with. He bought an 18" Fi BL which the seller claimed was "fully loaded". And he wants some help building a box for it. My 1st question is there a way to insure what options it was built with, like is there a serial number that can be looked up to see what it was originally bought with or a way you can tell what options it was built with? My next question is what is the optimal enclosure for these assuming it is fully loaded? He'll be running around 2500 watts (we'll set the gain to meet the power capabilities of the sub once we know what it truly is). He said he'd like to try a t-line but I don't want to spend the time getting one designed if it would be a waste of time, space, and wood! Thanks for any positive input or suggestions anyone has!