I have been talking to a couple of people recently who have been wanting to look at building a dual or twin t-case setup. Here is one of the better threads on a forum that I have come across that explains with pics what and how to replicate OTT's Kicker setup using a Vit trans and t-case with a Sierra t-case attached.
http://bbs.zuwharrie.com/content/topic,46349.0/all.html
DIY Kicker
Moderator: Committee