Jay, the basic requirements for M&M is simple: moisture, temperature, and spoors. Reletive humidity must be 70% or more at a surface, temperature above about 40 oF, and, of course spoors are always present. Keep in mind that a surface that is cold (such as a poorly insulated exterior wall) will have a higher reletive humidity since the air that contacts it will be cooled and thus able to hold less water.
The only controlable parameter here is moisture. You probably need to install a bath fan. Figure 1 CFM per sq. foot of floor space to get the recommended 8 air changes per hour (ACH). Don't vent it into the attic. Get a good quality fan such as a Panasonic or Fantech, they will be quiet enough to live with and will actually move the amount of air they are rated at; unlike the Home Depot variety. Check the pricing at www.tamtech.com and don't get suckered into paying more.