Images added with custom fields not showing in RSS feed

Hi,

I’m using a custom field (“featured image” – is a custom field within my theme) to add images into posts. I usually add a single image to one post and the image is also used as a thumbnail for the article. The problem is that the images don’t show up in the rss feed, even if the feed shows full text, not only excerpts. My feed is: http://www.traveltosun.com/feed/
I have searched the forums for similar problems but I couldn’t find a solution.
Did anyone had the same problem? How did you fixed it?

Thanks a lot!