The Search Page itself is working correctly and returning results as expected.
The RSS Feed asset does not show any data when I select the Search Page asset as the Listing Engine. I've tried adding query strings to the URL and Stored Search options but neither produces a working feed. So I tried the Search Page with a Paint Layout applied with the XML code to manually build an RSS feed but this still doesn't work. MS Outlook even says that the supplied URL is not a valid link so it doesn't add it to my RSS Feeds.
I thought (based on the link above) that perhaps the headers aren't sending correctly so I added that info to the Design. Not sure what is wrong but I've got a feeling is it the header information sent to the browser although it shows as "Content-Type: application/rss+xml" in the Chrome Dev Tools. My only indication for this is when viewing the page all I see is the code printed out but no browser formatting like you would expect from Chrome or IE (which adds some colouring and row formatting).
An Asset Listing page won't be able to provide the feeds that we need due to grouping and it producing multiple groups depending on the metadata tagging. A Search Page can provide this flexibility but a browser or feed reader doesn't read the page as an RSS feed.