Will a factory "behind the seat" subwoofer from 2015-2020 fit behind the seat for a 21-23 model F150? They're pretty cheap on Ebay and would like to throw one in my 22 Screw but I don't know if they'll physically fit.

 

Yep, should fit just fine, the rear insulation mat is a little different so would have to deal with that, plus maybe a few other things that might be in the way but nothing major, will bolt up the same. Just need to block off the horrible hole for the 21+ sub then add a decent aftermarket amp.

 

I like this idea. I had the Sony sub in my 17 and after swapping out that stock sub for an aftermarket 8" Kicker (and expanding the plastic box to fit it), along with adding a dedicated amp, it was a pretty good improvement for under $400. If this fits in the 21+ models it might not be a bad route.

Edit: after looking on ebay it appears that those boxes are min. $200, of which you then still need a better sub and additional amp. I am sure that you could find a small box for an 8" sub that would fit behind the seat for less than $200.