I have searched the web high and low and have not been able to find a tutorial or example of using jQuery to fade an InfoBox/InfoWindow in Google Maps not the content the actual
I do not think this is possible because Google does not provide an animation option.
Trying to get the Dom element will not work either. The ib variable is an google.maps.InfoWindow class not a DOM element. Since there is no public interface to get the DOM element for the info window you will not be able to access this yourself.
If you use console.log(ib.get("id"))
you will see that the ID is undefined.