I am migrating from libsyn to save $40 / month. I host all the videos on S3 saving lot of money. If you go live with your RSS feed pointing to libysyn when you switch over to your Rails rss feed, you must add:
xml.itunes :"new-feed-url", 'https://www.rubyplus.com/episodes.rss'
in index.rss.builder inside the channel tag to migrate successfully. This is in addition to logging in to your libshit account and changing the RSS feed to point to your new feed generated by your Rails app.