Somebody I know has used foam. Cut it roughly to the size of the intake,shove it in. Then trim any excess that peels up on the intake insides with a sharp knife. You can't use the foam with BIG cells, like the white packing foam. Something with a very small cellular structure works best, a good example is Dollar Tree Foam-core-board. It takes away most of the work, just get the shape approximately right. And plus, no damage if you ever want to remove it. It's friction fit.