Not sure how clearly you can see it in the pic, but I have vinyl cut to the size of the screen on my 40 gal with holes cut out for the heat lamps & air circulation.



I may have a better pic...

: Off to look for a better pic:

OK...Found one, you should be able to see it more clearly in this pic



I picked up the vinyl at Wal-Mart in the fabric dept for under $4.