I recently cracked a 40b. I'm going to break it down and use the good panels as lids for other tanks. A solid 40b can give you 4 lids (use 2 sides for one cover); they won't fit in the frame, but they'll cover the tank, just need the edges and corners sanded. 4 lids @ $40 if you get a tank at the $1/gallon sale, vs. $30-35 per lid if you buy them individually.