I tried it and thought it got hotter, I feel it keeps heat trapped inside.

But On the flip side Ive had mates that have tried it and are sure it runs cooler.

I was thinking about that as well and was thinking it would be good to leave a small gap near the motor so the air has somewhere to escape. So put the lexan on the fan but cut it back 1/8" from the motor. Worth a shot anyhow.