Hello George, I must say that all of the sealing for noise and fumes remains original at the closure of the Steel Cover. So any sealing will be as good as the rubber gasket that was originally there, on my car anyway. The 'Second'(fiberglass)cover over the first, will have 'breaks' along the seams. I have added a 1/2" thick heat/noise blanket under the full length of the entire firewall cover and 'bubble'. And since the Larger cover is no longer is removed, you could go even thicker on the blanket. Thanks for asking!
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