I knew about charcoal but not the newspaper part, I shall note it dow :- ) I have heard of people buying heaps of those tiny silica desiccant bags, but after the initial cleaning and airing out job. A proffesional solution could be a form of ozone treatment, I know it's used to remove smells in cars and furniture, even entire houses.
What is kitty litter sand made of? Some of it looks like "puffed" clay (heat treated). The kind forming lumps might be something else. Either way, all the smelly cases and cabinets I have had improved vastly after a thorough cleaning, and all the other tricks came as a second step. We should all have better storage spaces
