Adding a comment after Caoimhin is a bit superfluous, but I would agree with the posts above. The undercarriage seal that I typically see under a mobile is not a 6 mil poly, but does have teeny holes, is woven or has some function/ability to allow moisture vapor to pass.

I particularly like Phillip's comment about moisture diffusion/microbial amplification. Anyone know what that means?

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The apostrophe troll.