@AoW Do you need that custom feed, or could you rely on the one that Micro.blog generates for you? For example, make a new post for an episode and include the audio like this:
<audio controls="controls" src="https://your.cdn.network.example.com/episode-42.mp3" preload="metadata"></audio>
The podcast.xml template should identify that post as a podcast episode and include it in the feed.