There's a guide on Cloudy Nights (I think, link not to hand) about modifying a C11 - the chap uses Protostar's flocking paper.
No, it was another site:
http://www.darkatmospheres.com/music/C11_Project/ (see Section 3)
In the Cloudy Nights article, the chap uses felt lining:
http://www.cloudynights.com/item.php?item_id=2556