What are the measurements to put a sub box in a 1998 gmc sierra?

[Harrow101]

I am building a sub box for my 1998 gmc seirra extended cab and i would like to know the measurements to put them under my back seats

 

[knuckleheaf27]

http://www.supercrewsound.com/commerce/product.jsp?prodId=39&catId=24

This will save you allot of headache....