Your problem is easier to fix by using a larger water bowl but only fill it 1/4 to 1/3 of the way up, so when the snake climbs in the water doesn't overflow.
Also, I was concerned with the fire risk since OP's snake is in an elementary school classroom environment, based on other posts. So, all one of the kids has to do is put that heat lamp in slightly the wrong spot, and that cardboard is going to scorch. You're likely more careful with your setup.