I have done many windows to count. I have used rivets, screws, glue, adn tape. Two sided tape is by far the best and easiest to work with in my opinion. Any hardware store and places like Autozone will sell two sided tape. I like the grey 3m 5lbs. rated tape. All you have to do is cut out the window then clean up the edges or you can use trim to smooth them out also (available for about 5 bucks at Autozone). Once finished stick the window to back of the case door with the two sided tape and enjoy.
Just like my good buddy Bill Owens shows us here:
He adds a little more but you can clearly see how he mounts the window. Good Luck!!!