Bobbytwonames 5,000+ posts
Trigger Man!
So you're up against the old addages of:
1. Space makes bass.
2. There's no replacement for displacement
Rather simplified versions of Hoffman's Iron Law.
8" woofers just don't have much piston area and shallow mounts will have very limited excursion.
Your best bet would probably be to look into 4 very robust 8"s for under the seat just for the fact that it will be a better locadion/aiming of the woofers than up firing into the seat.
You may be able to lift the rear seats an inch or two to get a bit more box volume but this may be expensive and/or complex and depending on who is sitting back there it may not be practical.
I would avoid center console replacement. This is not a good location to get bass in a pickup truck.
I have an older F250 here and just have one back seat folded up and a box of around 3.75 cubic feet net behind that seat which can be removed if I need both back seats. This may be a good compromise depending how often you need ALL the passenger space. That location for a box allows you far better options for something with a large cone AND has enough depth to let you put in something with high excursion.
DO keep us posted with your results. This is a common question/issue.
I've seen two inch seat lifts for about $35.