I followed that URL and know it works but it doesn’t give me any information on how. That’s ok, though.
As you noticed, I defaulted the directory of the XML file to wp-content. I plan on adding an option to change the directory the file can be found in. I also plan an option to change the default file name (currently is the name of your blog with spaces replaced by underscores).
I made 2 changes to the plugin. One was to integrate your change to use url instead of wpurl. The other was to check to see if the XML file already exists before it runs the code to generate it. (Previously it was regenerating the file every time a page was loaded. The file check will cut down on page load time.) Both of these changes can be found in version 0.2 currently available at my website (https://nothing.golddave.com/?page_id=78).