Hi @kjetilhaugen,

I hope you are well today and thank you for your question.

The portfolio is fw-portfolio custom post type and you can add custom post type to RSS feed by developing custom code as described in the following pages.

http://www.wpbeginner.com/wp-tutorials/how-to-add-custom-post-types-to-your-main-wordpress-rss-feed/

http://www.wpbeginner.com/wp-tutorials/how-to-make-a-separate-rss-feed-for-each-custom-post-type-in-wordpress/

http://docs.pluginize.com/article/148-how-to-add-your-custom-post-type-to-rss-feeds

Best regards,
Shufflehound team