[villagetinker]

Frank,
I actually gave some of this to friends up North, with a cold attic wall, that seemed to have a continual mold problem. After painting with the ceramic additive, they claimed the problem was gone! I used it in one room and did notice an improvement, but not as dramatic as their experience.

OP,
It occurred to me that you might be able to solve the problem with additional air movement. I would try a fan above the doorway to move warm air from the house to the cold room. This would require cutting into the wall, installing grates, and wiring for a fan. Before going to all of that work, you may be able to get some inexpensive fan(s) had do a temporary install in the doorway to see if it helps. Theory is that you would be adding warm air (near the ceiling), and removing cold air (near the floor).
Other then additional insulation I have no other ideas.
Hope this helps.