I've tried a few different things like weight painting but it doesn't seem to do anything helpful unless I'm weight painting it incorrectly.
I was doing a quick rig of this model port when I came across this issue. There are 3 body meshes that go together and I tried to merge together to see if that would work but it does not.
It's only when you bend the model this issue occurs.
Here's the .blend file and textures in case you want to take a look. https://www.dropbox.com/sh/fgubdg3k7hz50pq/AACfqDFhF5ojuRpLGqNtu0M7a?dl=0