I’m using Alpine 12” Type R Thins placed under the seat. I imagine one might fit in an enclosure behind the seat. While an expensive driver as well, it is perhaps the cleanest tightest bass I’ve ever heard for a 12. It plays clean crossed over as high as 80. I tend to cross at 60 with a 12db slope, but that’s just me.
You mean like if you wanted to put the box behind the seat without interfering with the seat like the tw3 does?