flood & drain

okay if you are growing in rockwool on a flod and drain table I know you cover the top of the cube tostop algae but should I put down a coco mat then sit the cubes on top of the coco mat to keep my roots covered on my last grow I pot panda film over the whole table to cover the cube and the roots coming out of the bottom but I know there is a better way to cover the roots coming out the bottom the cubes hlp!!!!