i'd be willing to bet that it's not moisture,that your surrounds are very stiff from the cold and need some time to warm up.up here we have 2-3 months of 30-40 below 0 and i dont even turn on my stereo until the inside of the vehicle is warmed up.if your doors have something to channel the water away from the speakers,ditch the baffles or open up the back of them.they'll probably have better midbass if they can breathe alittle anyway