I wish I knew some way of making my own invisible collision model, rather than using just a big box. That's how it's done in most games I've played, IL-2 Sturmovik for example.
Easy.
Create a low poly, unskinned "match" of your model, bones and mesh-changing animations to match real model.
Use this as your player model, physics and all, just set to INVISIBLE.
Then your real model can be a visible but PASSABLE "ghost" positioned/rotated/animated every frame on top of it.
