The Dynomat and its ilk are good insulators but are lacking in anti-rust properties.

I've had good results using a sub-marine evaporative cooler coatings such as this brand.

https://www.bigronline.com/pps-packaging-submarine-sealer-qt-0411485.html

It is available at Wallyworld, Amazon, Tru-value and other hardware stores.

Apply it, let cure/dry and then add the Dynomat.

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