I just wanted to say that yes mold will build on anything unless you let it breathe air.
I haul styrofoam insulation panels for a log home company in Ohio and I also haul them from a company that makes them here in Ohio and they use the panels for roof insulation, and what they do is put the 4x8 panels down and put a vapor barier down then felt paper then shingles. And on the inside they cover it with 1x6 T&G pine. Any Log home I have ever been in there has never been any mold build up in the insulation.