this is an excellent starting point for custom recipes! i'd reccomend that you look at the docs on the wiki
http://bugs.calibre-ebook.com/wiki/RecipeTips
look at the version attached with some cleaning of your original suggestion and play with the code.
this source would be a good candidate for the html parsing as the RSS feeds does not contains many articles in the free content published in the different sections, however i think that subscribers will have an esier life by downloading the pdf!