I've had this happen not once but twice!
The first time, many of my childhood things (mostly books and papers) were in the basement, and sat there untouched for years. The basement wasn't exactly dry, and everything molded and mildewed.
The second time, I was living in a duplex, with four bedrooms. We had a large room on the lower level and we put our extra stuff in that room. I complained to the landlord from day one that the hot water pressure was significantly lacking. come to find out that there was indeed something wrong with it. A couple months after we moved everything in the room, I was going to organize everything, hang some stuff up, and whatnot. I took one step in the room, (I don't wear shoes indoors), and my foot got soaked. The carpet was completely trashed, and everything (all the paper products stored in the room) absorbed all that moister. The landlord tried to sue me after I moved out for damages to the water heater -- that was broken when I moved in. A fact that I pointed out when I moved in, and called weekly about. He dropped it.
These days, I don't have very many possessions, and what I do have is typically very rugged stuff. Most of my books I collect in PDF format and have stored in multiple locations.
Anyway, I never did answer the question! If manga counts as a comic book, then yes!