Looks good man, made my first "L" box last summer. I love the look of them and they still give you use and function of two rear seats.
You really need to seal these boxes, believe me. I used tons of filler and glue.
She hits nice and hard on the lows, obviously its not a ported box so it doesn't vibrate the truck to hell, but still worth it to me
I was going to install these Type R's under the rear seats, but they are too big for every box. So this was my solution