and i was wondering what angle the rear seats are in a wrx wagon...wanna build it so it fits flush to the seats. anyone know? thanks!

 

go to extant.com there is a amp and speaker company, they show you, or tell you, the right dimensions for corect speaker acoustics, no matter the shape, if you are going to build your own, check it out, they give you all sorts of info for building your own stuff.