Getting frost on subs and amp

Ive had frost on my subs and amps on and off over the past few weeks, usually when its under 15 degrees or so, its the worst when the car sits overnight. I did not go anywhere yesterday so the car sat all day, when I checked it today there was even more frost than usual. I scraped most of it off, and played the system at low vol for awhile. When I got where I was goin the frost had all gone away. The trunk doesnt leak as far as I can tell, and no other place in my car frosts up like that, not even the windows. My heater core leaks, so the floor on the passenger side of the car is frozen a little bit. Is it possible I could be getting some moisture in the air from that?? How bad is this for my system, its not actual ice, just frost.

thats from the humidity that is just in the air...when you know its going to be cold just put some visqueen or plastic over it in the trunk at night....like what people use to keep their plants from freezing.

The air is naturally dry in the winter, so when you get frost on your gear you know that the car is leaking moisture into the air.  Moisture on electronics is never a good thing.  Besides stopping the leak in the heater core, look into the spare tire well in the trunk and see if there is standing moisture, and if so see about sealing it off from road moisture and drying the trunk carpet out completely.  Also look at the rubber seal around the trunk lid and make sure it's not letting in melting snow.  Sometimes certain cars are best parked pointing uphill...

Thanks for the advice guys, it has warmed up to around 30 degrees today, and looks like it will be staying in that range for awhile. I had no frost this morning or anytime today. Some of my friends cars have done the same thing, so it just must be b/c its been so cold. I dont plan on fixing the heatercore anytime soon, or possibly ever, its about a 17 hour job b/c the whole dash must be dismantled, I will probably get rid of the car before I need to do that. There is no spare tire well in the car, but the carpet isnt wet anywhere, so im pretty sure there is no leak, it just must have been some moisture in the air.