If you're using Seriously Simple Podcasting to manage your podcast contents and RSS feeds then adding a second podcast would be just a matter of creating a new Series in your wp-admin dashboard and then filling in the corresponding podcast Feed Details for that new show.
In SSP each Series acts like it's own individual show, complete with its own RSS feed and archive page.
Note: The only thing that would be the same across all of your Podcasts in a single Castos account is the Slug that you chose when you signed up. This is unchangeable really from our end (it can be done but is quite an involved process for you because it affects all of your media file URLs). So your new show would live at yourslug.castos.com as well as your existing show, and all of the media file URLs would have the same https://episodes.castos.com/yourslug/file_name.mp3 format to them.