Im a big fan of the zuka tubes.
they arent for someone who is looking for whopping amounts of bass (unless you use more than 2 and they are the 10+ tubes)
I saw a demo a while ago where someone put 10x12" EL's into the rear of an astro van.
talk about serious bass !
but then again, why wouldnt there be with 10x12" subs pumping.
I like the simplicity of their design along with the amount of bass you do get for the size of it. but you can make your own easily enough, just go to a plumbing supply store, and grab a few pieces of their "throw away" tubing in the size your looking for. and slap a good sub in there with a tube port from the 1/2 point of the tube to the rear.
there are all sorts of ways to make a tube design, but that is the most basic method.