how can u see out the back window?

It doesn't block the back window at all from the driving position. The box and amp sit low enough that my field of view out the mirror is not impaired. I know it doesn't look like it from the pic, but it's true. The Zenclosures box I got sits low, and the amps are only about 2" tall so they don't even stick up taller than the top of the box (since they are mounted on the sloped side). I think on the Zenclosures website they have a pick taken from the rear view mirror so you can see. BTW I'm about 5'9" but I don't think my height would affect the field of view since the mirror angle would change if I were taller.

The only time it's difficult to see is when the sun is shining directly down on the amps and their reflection shows up in the mirror. But that's rare.