I just recently purchsed a cabin that sits VERY close to an active river so I'm sure there's high humidity in the area? I can NOT get rid of this horrible musty odor. If I open the doors up and windows, it will go away temporarily. I also purchsed (for several hundred dollars), a HEPA cabon air filter and another air filter that have been going full blast for months. For over a year, I've had a dehumidifier keeping the space at or around 45% humidity. None of these seem to make any difference. I open the door and WHAM, I'm hit in the face with that gross musty smell. I thought...maybe the walls' insulation? Nope. I had that all replaced with spray foam. No difference. The underside of the cabin is part basement (crushed rock floor) and part crawl space (dirt floor). Neither have any insulation and they have a few little vents to help with air ciculation. I don't think either of these spaces smell as bad as my house honestly. The one space that I'm questioning is the attic? I have fiberglass insulation up there. There's NO venting at all...and there's a huge hole in the ceiling where I had to take down the cheap pressboard in one area. Before I start a huge renovation effort to rip old insulation out or install an exhaust fan, I thought I'd check with the Pros first to see if there's something that should help? Do I need to replace the old insulation? PLEASE HELP! It's been driving me insane!!