Just cut a big hole in the tailgate, both sides if necessary, to be able to access all the components so you can unbolt your window. Sawzall will work fine, just make sure you use a short blade so you don't jab it into anything on the inside of the door. But for less vibration use a high speed cutter that runs off an air compressor(if you have one). They usually use a 3" cutting disc that turns at like 20,000 RPM, and they work good. Or an air powered sheet metal nibbler will work even better once you get a hole started. I used both of these to cut open the outside of my doors on my car after it was hit in the side to do the same thing-save the glass.