[Greg S]

The sub tub is a great idea, my only concern would be the air space in it. At 3.8 cu. ft. it is way too much airspace for most car audio subs.

For example your sub, the Kicker l7 is designed for

sealed box volume: 1.25-2.0 cu. ft.
or
ported box volume: 1.75-3.25 cu. ft.

And those specs are on the somewhat high side for many car audio subs.

My other concern is the price. It's not completely out of line for a custom fiberglass sub enclosure but you could have a custom enclosure build for the same price that has the correct airspace for your sub and it will sound much better that way.

i know I could build the enclosure and install the amp for that price no problem.

 

[Greg S]

If you listen to a bit of everything then a sealed enclosure will actually work better. It will go lower and have a more linear sound but it will not get as loud as a ported enclosure at the port tuning frequency. Sealed enclosures are also a lot more forgiving when you over power them as you can hear the distortion build up gradually and they handle a lot more power as well. The down side to them is that they do require more power to get and equal volume level as compared to a ported enclosure.