OnSave Event not seen if tool window closed

I'm completely new to VS extensions.  I need hook into the OnBeforeSave event so I followed an example on the docs site which creates and RDTEventsExplorer. This all works fine if the tool window the example uses, is first opened from the View->OtherWindows menu.  It can then be closed and the events are still captured.  However, if the tool window is never opened the events are not seen.  So my question is how do I create an extension with no tool windows or menus which reacts to the OnBeforeSave event?  Where do I put the code which implements "IVsRunningDocTableEvents"?  Anyone know?