Washing Question: Clothes smell bad, smell won't come out.

Hey, r/fashion, I'm a college student with a set of clothing that I don't intend on replacing anytime soon for financial reasons. Over the summer, I leave some of my clothes with a friend so I don't have to take it all home (it's a long trek.) Last summer, I made the mistake of keeping some of them in a duffle bag that smelled strongly of rubber and, well, the inside of a duffle bag. Nothing putrid or horrendous, but it's not the most pleasant smell, and despite my frequent washing, it simply never comes out.

Before I employ a random method from google, do you have any tips (preferably cheap) that might remove this dull smell from my clothes? Thanks.