Not to revive this thread. But, the sub/amp combo boxes have come a long way in the last 10 years.
In high school I had 2 12” JL low profile subs behind the seat of my truck. Now, I just have a little 10” Rockford fosgate all in one unit in my Civic. Thing hits HARD… I was expecting just a little extra thump, but i actually needed to turn it down quite a bit. Something that I almost overlooked and I bet a lot of people would overlook as well since they were pretty lackluster a decade ago. Stupid easy to install and it has the LOC built into the box, so I was able to retain my factory radio without any extra wiring.
They’re pretty affordable too. I think I paid like $380 for it… which is pretty cheap considering it has everything. Not nearly as full and boomy as an actual setup with a ported box. But more then enough for a stock sound system or someone on a budget.