mold on center console

so i go to start putting the body back together on my 86 and i find mold inside the car ??? wtf?? i got no idea how it got inside the car. she has been sittting a little while but has been sealed up. there was mold on part of the drivers seat and the center console. how could this off happened? what should i use to clean it up with and how do i prevent this from occuring again? thanks for the help.


jeremy