Compact sub recommendations

[Green Giant]

Are there any compact sub units that will improve the sound, enough to actually buy one and have fitted?
We have upgraded the front door and dash speakers( to Alpine) and have had the front doors sound deadening kit fitted.
No room under our front seats for the Alpine seat base sub, so thinking of a small sub unit that could be mounted near the rear of van, but don’t want to take up too much space
ta

 

[The Flying Scotsman]

Like you I have very little space to fit a sub.
I have the smaller 8” version of this and it’s ok. It fits below my seat above the diesel heater pipes.
I plan to upgrade to this more powerful and bigger sub/amp in the future.

Pardon our interruption...

 

[Howzat]

I got the Kenwood KSC-SW11 in 2021 to fill out the sound and is still working fine although it's now been superceded with the Kenwood KSC-PSW7EQ.
Fits under the drivers seat in my van.
It's not window rattling bass by any stretch of the imagination but it's overall effect is very noticable when turned off/down.

 

[Green Giant]

Cheers, I’ll look at both of these subs and have a look at where they could be mounted