You gain around 3 or so inches in depth. The opening is about 9 or so inches high. You need to seal up each side of the cavity when you cut it out as it is open to the exterior. Be careful of the fuel tank lines running through the cavity on the drivers side.
Mine when I got it finished with 10" subs.
[This message has been edited by Khw (edited 06-06-2010).]