Please accept my explanation of the GFCI operation. The circuits in and out of an appliance run through a torroid transformer. When the current going into the appliance is .006 amps more than the current coming out, the device "assumes" that the current is faulting to ground through someones body and the transformer generates a current which in turn activates a relay opening the circut within 25 to 30 miliseconds. From what I have read, moisture is causing a current fault to ground and the device is acting as designed. Try a using a blow dryer on suspect areas to dry them out. That may solve the problem.
Bill..