I don't have the box dimensions but at the time it was built the measurements were very slightly larger than JL recommends for a dual 10" setup. As I said, They custom built it to fit behind the seat and had to make a couple design changes along the way to allow the seat to fully fold up. getting measurements is difficult now because it's integrated with the rear material and I'd have to pull it away to measure the box. If you take it to a reputable stereo shop I'm sure they can do it for you. If not...I used Car Toys in Portland Oregon, 503-788-5777 ask for Scott and he should be able to talk your installer through it. Sound quality is very subjective based on personal preference and hearing senstivity...to my ears it sounds fantastic and it's the right balance between perfect=thousands more and really really good = 7k. I used Focal, Zen and JL audio throughout the build.
I am the installer. Just wanted to be sure the seat will fold up and not hit the sub without the kit that moves the seat forward. Thanks for the info!