The hard part about adding bass to a pickup is not the bass. It is that a truck is a tool, and the space in it is already spoken for. A conventional box goes in the back seat footwell or the bed, and either way something the owner actually uses stops fitting.
This Tacoma came in for exactly that problem: the factory system had no low end worth the name, and the owner was not willing to trade the cab or the bed to fix it.
A box shaped like the hole
A Stealthbox is a vehicle-specific enclosure: JL Audio moulds the box to the contours of one particular cavity in one particular vehicle. It looks like an odd shape sitting on a bench because it is the negative of a space you cannot see.
The point of it is enclosure volume. A subwoofer's low-end performance is set as much by the sealed air behind the cone as by the driver itself, and a generic box that has been trimmed down to fit somewhere it was never meant to go gives up exactly that. Because this one is built around the void behind the rear seat, it uses volume that was already being wasted — instead of taking volume from somewhere the owner wanted.
In and out of sight
Fitted, it sits against the rear cab wall behind the seat, finished in a carpet that matches the factory trim. The rear seat still folds and still carries what it carried before. The bed is untouched. Nothing was cut.
What it changed
The result is the bottom octave the factory system never had — enough to give kick drums and bass lines a body, without the boom that makes a truck tiring on a long drive. It is tuned for a daily driver, which means it fills in what was missing rather than announcing itself.
Nothing was given up to get it. That is the whole appeal of doing it this way.