My first sub was the original 6" dual sub bazooka tube.... way back in 88 or 89.
Back then, they required very little power & sounded pretty good. Now, they have amps built in & all sorts of options.
No boxes to build, but you'll need to secure it down so it doesn't roll all over the place.
For reg cab trucks, you could probably get 2x 10" behind the seat as long as their parameters require a small volume box... or you could use shallow mount subs to save a little depth.
Back in the day, I installed 4x 12" behind the seat of an s-10 reg cab for a guy. There wasn't nearly enough air volume for the subs & I thought they sounded like poop, but he was happy to show off his 4x 12"s.
It all depends on how loud vs how clean you want it to sound. You could easily grab a cheap set of subs and a cheap amp that will be loud but it will probably sound like an elephant farting in a phone booth.
I outgrew the loud phase real quickly & focus more on the sound quality, staging & noise elimination.
Check out Crutchfield's website too, great place for info & reviews.