Looking to make a box for 2 sundown sa12 v3

[Zidane]

Looking to make a sub box for my 2 sundown sa12 v3 there rated 1500rms each dual 2ohm and wired to 1ohm and there on a taramps 3k 1ohm amp. They are in a 2008 Hyundai sonata wired to a line output to rca off the factory sub. Has an aftermarket radio but seems to play best off the line output converter. Looking to make them louder and hit better in a new box thanks 

[EricM9104]

4cubes @ 35hz...

How does the LOC provide better sound from an aftermarket radio? Are running a 3k amp at .5ohms with no upgraded electrical?