Help whit box size for pickup

[bigbeto]

Hi, i have 1 kicker CVR 12" 4ohm, y want to know the best size of the box for my chevy silverado 2006 2doors work truck model. i want the bass sound inside and outside of the truck i have right now 1 box the size is 20wx14hx5d2x9d1 but i cant hear a good sound. i want help.

[55437Audio]

all i can say is when i had my subs in my truck the bigger the box the better the sound... not much else you can do in a 2d truck, just make em as big as you can