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You can get metal "screens". I use this one (also for 20 long), and it would definitely support the weight of a cat. I use a ceramic heat bulb, not sure if actual heat lights would get it too hot, but my ceramic bulb does not heat it up at all.

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

EDIT: So sorry, did not realize this post was from November. I'm sure you've figured something out by now.