Car Audio
From GummyCarbs
Soundproofing
Decoupler
Carpet Padding
Most foam carpet padding is open cell, which will absorb and hold any water that leaks in or accumulates via condensation. Closed-cell foam is better.
Noico WP 150 1/6" thick, closed-cell polyethylene foam seems to be discontinued.
Lifeproof 6x9 Waterproof 5/16" thick rug pad is available from Home Depot for $0.95 per square foot.