I've created an interior box to fit inside the outer 'shell' of the carriage. I felt this was the easiest method to do for this as simply extruding the existing faces inwards presented me with more problems than solutions. This section will be visible to the player during the introductory scene, so it's important that I get the details right and that all the face normals are facing the right way.
I've created a luggage rack and wheel supports, using my old model as a guide.
Now with the added interior, I'm having another attempt at 'wrecking' the carriage. When the player sees the wrecked carriage, the door will be open to appear as though they have just climbed out.