Here is an updated copy of the drawing. I tried to include all the dimensions.
I think it is confusing so I tried to color code some of it.
The magenta area at the top is 18in high. The green part is a small arm rest. It will be 15in high. The part to the left that is completely white in the top view is slanted down for my AC controls in my truck. It will not be part of the box. I will be using 3/4 inch MDF for the whole box. Also subs are 12.5 inches wide.
Edit 1: I forgot one thing. The box will be 15 inches wide.
Edit 2: Some of my dimensions were wrong so I updated that.