Posted for "martin heisler" <martinheisler@hotmail.com>:

one way to make up trim.
many automotive upholstery shops have a treated , solid ,door panel cardboard
used for custom work.
use some heavy brown wrapping paper , tape to the outside of the window and trace the window shape on to the paper.
cut out the shape , make the border as wide as you want.
trace this on to the cardboard and cut out with an exacto knife,
have this ring upholstered and this can be glued on to inside of the window.