Need help with modeling

[KelenStardragon]

So I've discovered that when creating clothing models, you should not duplicate a mesh and mirror it to create the inside of the model, because it can have disastrous results. For one thing, it completely messes up the UV wrapping, and secondly, the duplicate vertices aren't parented to the correct bones, so though they look fine with an unanimated model, as soon as you see it ingame, it messes everything up. So does anyone know a way to create the inside of clothes without messing it up like that? Cuz otherwise, parts of the clothes will be invisible from the underside. Basically, I'm trying to make a trench coat, but I don't know how to set it so that you can see the inside of it as well as the outside.