At first I imported the files into the web-cpan repository , and patched it there. Then I wrote a few patches by working on the working copy of a checkout from the svn.perl.org repository, but that turned out not to scale too well. Eventually I decided to use svk instead, and wrote two patches using it.
I kept some notes in a text file about my progress. Here they are:
Ask Bjørn Hansen (the XML::RSS maintainer) has already applied a patch, but there are more in the Request Tracker. And there are still a lot of bugs to cover.