Looking at the service manual it seems that the rear seatbacks fold down allowing access to the back cab panel. You can see and feel the latch when you raise the cushion (look behind and down from the headrest). You need to pull up on the latch to release the back from the cab panel. This is from the service manual:
The Crew Cab rear seat is a 40/60 split bench style with folding cushions and optional folding armrest with cup holder. The backrests are fixed to the rear cab panel by latches that can be accessed from behind only for service allowing the backrest to fold down. The backrest latches are accessible only when the seat cushion is folded upright.
Release the backrest latch.
From behind the backrest, pull up on the latch release and pull the backrest forward.
Release the cushion latch and lower the cushion and backrest.
I tried to pull up on the latch but cannot get it to release. Has anyone been able to do this? I want to install an amp behind there so I need access.
I was worried about my last amp (only a 500 watt) that was bolted to the rear wall of a regular cab. It got so hot I thought it might be a fire hazard with the carpet back there. And that had around 6-8" between the seat and the amp. I couldn't imagine just sandwiching it between the seat and rear wall...seems like it would go into safe mode quite quickly...