according to my calc..if it is a quarterwave tline.... ur tuned to 13.3333~ hz... thats really low....
unless thast the FS of your sub... OR... if this is for HT setup... i wouldnt tune that low...
if u are gona build that box fix ur corners by puting 45s in there..
info on quaterwave tlines here
http://www.stevemeadedesigns.com/board/topic/1828-quarter-wave-t-line-tutorial-updated/
Edit: tlines take up a alota room... im using a tline in my truck... tuned to 40 hz... low end is a bit lacking for me.. i would tune to 30.. but be carefull cuz there is no back pressure in a tline box... you could easliy destroy teh sub...
from experience.. i would rather build a regular box... i will only use a tline for anything below 800w rms...