Hiya! I just got my own Rubies trooper helmet, and watched a video that suggested to use velcro and cut pieces from a see through dark tinted document protector and glue. That sounds good to me so that's what I'll be doing. He doesn't show this in the video but does say that in the description. Also he mentions sanding, but I can't see why for a piece of plastic from a document protector. https://youtu.be/sDahNMbRY3c
Hope this helps!