As long as you have driver and passenger side mirrors, the rear windows will be fine.
The legal limit for the Driver and Passenger Side windows are 70% visability.
"The law prohibits any person from driving any motor vehicle with any object or material placed, displayed, installed, affixed, or applied upon the windshield or side or rear windows, with certain limited exceptions.
However, legislation signed into law effective January 1, 1999, exempts from the above prohibition specified clear, colorless, and transparent material that is installed, affixed, or applied to the front driver and passenger side windows for the specific purpose of reducing ultraviolet rays. If, as, or when this material becomes torn, bubbled or otherwise worn, it must be removed or replaced."