Well since I made my window I therefore had to make my own blowhole in the window and I found that a 3" holesaw works best. Mine came out perfect. I wouldn't recommend doing it with anything else because trust me, this stuff cracks easy.
The stuff cuts pretty easy. I used a drill to make the four mounting holes and one larger starter hole and cut out the rest with a fine toothed metal cutting blade in a jig-saw (the same thing I used to cut the hole in the side panel for the window). I then lightly sanded the endges with a fine sandpaper. Make sure you do not over tighten the mounting screws as Lexan can crack. Also tape around the hole so you do not scratch the Lexan with the jig-saw.
Her is a picture of the window. Of course you can not see the detail of the cut, but yes I have done it.