Re: Tank Cover for Humidity
You could buy a cheap picture frame. They run a dollar at dollar tree, for instance.
If you're lucky you could find some already in the dimensions you need.
Otherwise, it's super thin and pretty easy to cut if you have a glass scorer. Then you can just fit the glass pieces on top of the screen, or remove the screen and silicone a single piece in place, but again it is thin, I'd feel safer setting them on the screen.
I'm using this method for a few of my 12" exo-terra cubes.