Skirts with trains

I don't know if this will help as I haven't tried it yet myself, but Tea 'n' Moon has this to say:

1. Subdivide. Select your whole transfer mesh, hit W, select subdivide, and in the subdivide options increase the number of cuts to 3 (or more).

2. Edit the shape of your transfer mesh. If you're transferring to a new mesh that has a much wider sleeve or much wider skirt, it's helpful to use proportional editing to change the shape of your transfer mesh to closely resemble your new mesh.

3. In Blender 2.76+ retirement with different calculation methods for weight transfers. The Projected face interpolated, Nearest face interpolated, and Nearest Face Vertex can all give better or worse results depending on your mesh.

It's the resizing of the reference mesh that I mostly want you to see. Again, I haven't tried it myself so I can't vouch for it. I've been working on a conversion that has a train, though not as long of a train as yours, and I transferred the weights from the Grim Reaper mesh, which does not have a train. The result is that the mesh animates okay (may need some tweaking) but the train is stiff. It doesn't move naturally. For instance, the sim bends his knees and the train flips up. I don't know at this point if tweaking the weights will help or not. I don't think it's possible for a train to move naturally in the game, anyway. I think there are limitations in the game's engine that prevent natural fabric movement.

Edited because, as usual, I forgot something. SLYD has a tutorial that explains testing a mesh's behavior in Blender. It explains how to edit the weight paint to control how a mesh moves and morphs.