Product review (5 stars): Perfect fit for our model 600 humidifier
Perfect fit for our model 600 humidifier.  One thing to be very aware of though.  There is a colored spot on one end of the panel.  Make sure you put the panel in with this spot on the TOP.  If you don't, you'll have water leaking all over your basement floor.  As long as you put the panel in with the colored spot on top, it will function perfectly!  Another way you can tell which way the panel should be installed is to look closely at the direction the louvers on the filter are going.  If they're going in an upward slant, this is the right side up; downward slant is upside down and will cause leaks.  Hope this helps all my fellow do-it-yourselfers!