I have an Uncle who left a damp rag inside his Avalanche, which sat closed up the entire winter. Now, it has a terrible mildew smell.

Anyone have any suggestions on how to get rid of this odor, or what he might try?

Thanks

 

you can try a car wash company that does interior detailing,they have industrial type sh@t that works wonders and in most cases doesn't wear off just make sure you point out the spot that rag was so they can treat it better than regular

 

A detail shop could use an extractor to clean and wet vac the carpet, seats (depending on what material they are) and headliner, some time that is enough, depending on where the towel was sitting. If it was on the floor he may want to get new carpet, this has happened to a few customers. There are also industrial sprays, but many times the smell comes back.