putting a subwoofer under or in the back of the rear seats

I have a 2011 Tacoma and it has the JBL sound system with one sub behind the rear seat but I want to either put another one or upgrade the whole system. Does anyone have any advice on doing this?

 

Tons of options,
Everything will depend on your skill, Budget and time your wanting to spend on the desired outcome.

I have a wide range of package options to meet even the biggest audiophiles requirements but also have entry lvl sound quality items as well

 

Lots of work. Pretty much requires cutting sheet metal unless you're REALLY good with wood. I have no complaints with the amount of bass I got out of it.

 

That looks pretty legit.

 

We are a small group....the USSC (Under Seat Subwoofer Club). It's a great way to save space but it's a pain in the ass install. Trust me. I've helped a few get started with the endeavor. More info can be found in this thread.
https://www.tacomaworld.com/threads/under-seat-subwoofer-club-ussc.234155/

I'm currently running two 8s sealed down there. Picture shows Elemental Designs e3.8 subs but I'm now running some CSS Trio 8 subs.

 

How about shallow mount 10's. They would work, right?? I listen to heavy metal, and not much on big banging bass, unless it's that bad ass drum bass that Fear Factory puts out, and so forth.. Any thoughts on subs??