There are a variety of anti-fog solutions available for automotive use, have you tried any of them? One that I use (for automotive) is Rain-X, it seems effective there.
This isn't as simple as a chemical solution or clear film, but maybe you could look into an air-knife system that would blow away any condesation from your reader and labeled products.
MadMango "Probable impossibilities are to be preferred to improbable possibilities."
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