It's difficult to explain but this room, which is heated somewhat in the winter, is actually entirely wood framed, both walls and ceiling, with a dirt floor since we stack up to 12 cords of wood in there, so there is moisture for sure, but the surround area (walls and ceiling) are not in contact with dirt at all. The issue in my case, is that the moisture vapor charged air is getting past the metal and trapped against the plastic, and running down the rake of the ceiling to the wall. I once participated in the construction of a huge lumber kiln, and this is where first hand, I realized that you have to use sealant at your metal laps when you have extreme moisture. Also, another point to consider is that if you're heating your shop, then turning the heat off, then heating it again, and especially if you live in an area like I do where it can drop to -35 degrees, these hot cold cycles will cause condensation on your interior metal surfaces, both front and back, because if you have plastic, the plastic prevents the insulation, if blown in, from coming into contact with the back side ribs of your metal, so you have an air space that would allow moisture to collect. Probably not much, but when you don't use plastic, and instead seal all your joints, now your blown in can get down into the rib voids and prevent air space. Even if you did get moisture there, it could still escape up through the insulation, and eventually through your attic vents.
