Creating Custom Preferences

Ok, I've been staring at this all morning and can't figure out why this isn't working. I've successfully created a custom test step and action and now I want to be able to give my users some flexibility in how they work. These are really global changes so I want to add my own preferences page.

I've created a new class which implements PrefsFactory. This class creates an instance of the class which implements Prefs and has the code to build the form and get/set the preferences.

Factory Class

public class ExportXmlPrefsFactory implements PrefsFactory {
    public Prefs createPrefs() {
        return new ExportXmlPrefs("Export XML");
    }
}

factories.xml

<tns:factory id="ExportXmlPrefs" factoryType="com.eviware.soapui.actions.PrefsFactory" factoryClass="com.mycompany.ExportXmlPrefs"/>

When I copy the jar to ext and re-start, I don't see anything in the preferences dialog. Any idea what I might be missing? I'd expect to at least see my label ("Export XML") even if the form itself isn't working yet.