Box volume check and help

Here's my equipment to be installed

2 8w7
C3 components
C2 dash
Alpine CDE-hd149bt
HD900/5

I need a box volume of 1.87 cu. ft. I've attached some pictures of my box shape but I wanted to double check my calculations. The whole measure twice cut once. I'll be using 3/4 MDF I can change all dementions except the lenght which is 31" outside or 29.5 inside. I really need the help.