That trucks been gone for over a year. Flipped it. The seat did fully close but i had used thinner mdf, if i remember right it was 1/2". I can look for a few videos i have with the seat down and latched but itll take me a while to find.
If you're able to make the custom box for a 12" go for it. I myself went with the 12 over a 10 for more bass. I've loved it since I got it in and there's no downsides I have to it. Yes the space is tight but it fits nicely.
Had many people tell me a 12" sub wouldn't fit under the seat in the storage compartment. Got it in a few months ago and completed forgot to post the build update. I'll post some newer pictures of the wires cleaned up later on.
The Memphis sub I chose is a shallow mount and is only 3" in depth. There was also a 12" JBL that was a 3" shallow mount. But I know the Memphis subs hit harder so thats why I went with it. Not sure when I'll start building a custom box for it but should be some time in the next month or 2.
I've seen a lot of people putting a kicker or pioneer sub behind the rear seats. But has anyone built a box into the storage compartment below the seat yet? I"m about to do so myself and am looking for the max depth of it. So far I've measured and its about about 6 1/2" deep (without pulling up...