Today I installed the ad glasses. I was asked to document how I did it. I called GPH, and they said you have to clearance the rubber for the corners, or they make an acrylic ad glass with radius corners. I suspected this was to be the case. Here's what I did. Start by marking the center of the opening. Start installing the rubber around the opening starting at the mark. Trim the excess. Complete the install of the rubber all the way around.