This would require making a hole in the fins. Then much of the air intended to go through the entire coil would crowd through the hole, greatly decreasing the coil's heat-exchanging efficiency. CDX is a rating given to some plywood. The faces of ordinary plywood are rated from A, which has no imperfections such as knots, to D, the other extreme indicating open knotholes. X is the designation for exterior grade plywood that uses water-resistant glue to adhere the plys.
Marine plywood is glued together using waterproof glue.
OSB is short for oriented strand board. While plywood is made of glued sheets of wood, OSB is made of wood chips glued together, which involves less waste, creates a stronger product and costs less. OSB is available in interior or exterior grade. Even so, a lot of people still prefer the plywood since it has stood the test of time. Many credit furniture maker John Henry Belter as the inventor of plywood.