I have a Kicker L5 12" in a kicker enclosure sitting on the rear seat in my truck, powered by a MTX 600w rms mono-amp. I know this isnt a good sounding sub, but it is loud and, if I crank it, can give the feeling of "too much bass" for my truck (Explorer sport trac 4-door). I like a lot of bass most of the time, and the option of having too much when I feel like it.

I am getting shallow mount subs to put behind and/or under the rear seat because I dont want a sub taking up half the rear bench. But I want to keep the volume and air-moving power the L5 has. Is this possible with shallow mount subs? I plan on getting a bigger amp too if necessary.

I want the best shallow mounts...so I want to see what's recommended. I've mainly been looking at the JL Audio TW3 (10s or 12s) or TW5 (13"), and Alpine SWR 10s or 12s. These are thin enough to fit in a box behind the rear seat. I've seen sub boxes specific for my truck, but only for 2 10s at best (behind seat). I will probably modify or build a custom box to fit 2 shallow 12s or 1-2 13"+.
Will I be able to match or exceed the output/volume my L5 has now?