Adding Content:media to rss feeds

Hi,

Recently signed up to mail chimp which takes my rss feed into a news letter. Problem is to format the images, it needs them to be formatted media:content in the rss feed as in (http://blog.mailchimp.com/rss-to-email-enhancement-for-publishers/). I have tried and tried but cant seem to get this. Tried installing the media rss plugin but it does not work. Any ideas please???

Just on a side point, any way to preserve bold formatting in the rss excerpt and stop featured images from cropping in the rss excerpt?