After looking into making my own incubator and liking the idea of using a plastic cooler then just breaking down and just bought a genesis 1588 incubator because of reviews and price but didn't like the idea of it being foam. I felt like it is an investment and would be worth protecting. So I began looking for some sort of coating to protect the foam and found this http://www.smooth-on.com/Epoxy-Coatings-EPS/c1397_1400/index.html
I think I'm going to go ahead and try it. Once dry it is like a plastic coating that is resistant to the heat of the incubator and the humidity. I've read of people coating the inside with silicone but think this will be just as good.