How do i save to forwards to separate files according to subject

What I have so far is:

:0
 * ^From.*gerber
 * ^Subject:(.*:)? *\/[^ :]+\<.*
 {
  SUBJECT=$MATCH
  # use $HOME variable in case admins reorganize the system and move it
  STORIES=$HOME/public-web/Stories


  :0
  * SUBJECT ?? /
  SUBJECT=| echo "$SUBJECT" | tr / %


  :0bc:
  $STORIES/"$SUBJECT"
 }

The thing is that it creates a file with the subject name but it has the 
Fwd: and it has spaces.  What I need is the fw or fwd removed and the 
spaces turned into "_".  I am assuming that i would use the "s/\s/_/" but 
not really sure about that nor do i know where to put it.

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