A lot of the musty order of cases comes from mold and mildew growing in your case. Keep it clean and dry; leave it open when it's not in use. Some silica gel or activated charcoal kept in the case will absorb smells and moisture (replace the stuff periodically).
Woodshell cases that develop a persistent case of the musty yucks usually cannot be deodorized short of using them for kindling.
I know a bassonist who puts orange peel in his case. I think that it has something to do with the moisture level in his case (I live in dry Colorado) but it does always smell good.
I remember a kid in middle school had dryer sheets in his case. You could also use a car freshener, a little pine tree hanging from the top of your case when you open it.
I vacuum smelly cases and spritz them with "Fabreeze". A dryer sheet inside the case can also be helpful.
Dan Schultz
"The Village Tinker" http://www.thevillagetinker.com" target="_blank
Current 'stable'... Rudolf Meinl 5/4, Marzan (by Willson) euph, King 2341, Alphorn, and other strange stuff.