Has anyone tried using gatorboard for masking?
From what I understand, it is extremely rigid while still light. Would it still be light enough for friction to hold it up?
I was thinking of using your same design with 1/2" gatorboard covered with this material http://www.fpi-protostar.com/flock.htm
Since my screen is 118", I think the 1/2" should work better than 3/8" to avoid any warping. There is a gap of 1" from the front of the frame to the screen, so there would still be some spacing in back of the masking without it touching the screen material.
I have a Carada precision screen, and supposedly the prostar material matches the Carada "black hole" velvet very closely.
I've found a local shop that will cut me multiple pieces of gatorboard to size so that I can build several panels for 2.39:1 or 2.35:1 or 4:3. Total cost for all the boards cut by them to size will be $116. It looks like roughly another $100 for the prostar material for all 6 panels.
I'm still putting together my home theater and have several things going on, so this project will have to wait another week or so, but looking forward to it.