Transmission Line Advanced Slot Ported

That appears to be a standard ported box, not a transmission line.  The port just happens to be long and goes through some turns.  Build a slot-ported box, and if the port length is long you can turn it back and forth like this one is.Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

Does any one know where to find some good plans for a transmission line enclosure?

First off, good call, stevdart. It's NOT a TL at all. It's a slot loaded box, and nothing more special than that. There are none. There is no real science to TL design. I know, I've built 5, with woofers from 10 Eclipse Ti's to 18 inch KSC imports... Stuffed, unstufed, box coupled, true lines... MANY attempts at the TL, some with good results, some not quite so acceptable. PM me your e-mail address, and I'll see if I can locate some of the plans I used...It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

damn that sucks because everybody tells me these boxes are best out there and they sound a hole lot better than round ports.  i still want some plans so i can play around with it ,thanks.