Mold is not uncommon in conditions that occur with fridges and freezers. I'd definitely coat that bare wood with Urethane or your favorite finish and then clean it once in a while with a bit of bleach cleaner.
And I'm curious about that "Mold Armor" that RedBeard mentions. Might be worth looking into for a recurring problem area.
Day after day, it reappears. Night after night my heartbeat shows the fear. Ghosts appear and fade away. Come back another day.