Thats an awesome DIY setup for a lid and I was just saying that it can crash it yes a little far fetched but I know some people who don't know too much about fish do some crazy stuff.
I use pexiglass because I'm cheap lol
You can actually use any thin plastic....the egg crate really does keep the plastic from curling. I even use the thin plastic light box diffuser panels....easy to score and cut, cheap.