I like the Makerbot clips made by berserkerscientist but i wanted the windows to be fitted. I added support to make the window sit the same height as the bottom of the opening. I also made a top window clip so that the window wouldn't flap around when the printer get moving a little.

Print 2 of the Things to get 2 tops and 2 bottoms. The M will show you which 1 is the top and the bottom.

Place a sheet of paper over each opening and trace the window shape. I taped the paper over the outside and then traced from the inside with a fine point sharpie. Then trace the size on to the 1.5mm acrylic sheet. I used an Exacto knife to cut the shape out.

Fit the window into the 4 clips. The tension of the sheet will hold the top clips in place.