I am going to be heating my darkroom with my Serenity pellet stove. It's already installed in the space I'm going to be using so I can't afford to switch it out for anything else. Plus it's a great little heater so no interest in doing so! Anyway, I need to black out the viewing window because it's a darkroom. Plus, I'd rather not do so permanently. Given the heat I can't just put some blackout paper over the door, or some other combustible or meltable material. Any ideas?