box help can someone check this

[robby512]

http://s1325.photobucket.com/user/robby5121/media/123_zps30ec637c.png.html?sort=3&o=0

i made a box for 2 sundown e 12's

outer dimensions are length 30 width 14.5 length is 18.5

this is where i dont understand

my port is 3 inches wide all the way around 10 inches deep

and has an extension that is 2.50 inches long

i think i did roughly 14 inches per cubic foot

did i make the port right and what did i tune it to?

and it should be around 3.38 cubic feet after displacement

And what does putting the 45's in the corners do?