Here's a t-line I built a while back for a JBL GTO 10, D4. It's in prime but could be painted any color or covered with any material. And, it's for sale.
↑ I started it for a Fosgate P1 I had but the JBL has the same Fs as the Fosgate and is a much more durable speaker.
↑ Second layer of baffle.
↑ Third layer of baffle. Mostly cosmetic.
↑ Speaker wire epoxied and covered with vinyl body filler to minimize line interference.
↑ In prime. Once I decide what to do with the ornamental panel on the front, the screw holes will be filled and covered over. The panel could be raised ½" or so to add LEDs behind it or it could be laminated to add strength.
Next will be a line for a GTO 8 that I have laying around. I'll probably use it for a computer sub but I might sell it. Then, when the SA-15 I ordered comes in, a line for it. If it works out well, I'll sell it, remove the seat from my truck and put two X-15s in a permanently mounted t-line.
EDIT: If anyone knows why this site won't embed videos or why I'm too stupid to make it work... please let me know.