I have seen in thread(s) about adding poy fill to the factory sub box.
I have a 08 SCREW KR, obviously with the factory sub & NAV.
May seem like a dumb question, but, how much is the right amount to add?
Thanks in advance for any advice.

 

The rule of thumb is 1lb per cubic foot. Not sure how large the factory box is, but I would lightly stuff it and see how you like it. The poly should increase low-end extension.

 

Thank you Ray!