I have added interiors to all my F7s'.
Use PEV Trainz Mesh Viewer to see all the attachment points.
It's quite an endevor to accomplish all this. I also added the
F7 shell which is yet another story. The shell provided by Auran
doesn't quite attatch correctly and requires a lot of time to get
right.
Be sure to back up what your doing so you can easily undo and
start over.
Once you get the interior and shell correct for one F7, it will
work for all of them. I just requires a boat load of config file edits.
AL