Manually inserting enclosure

When Writing a Post, in the Advanced interface, scroll down to “Custom Fields” and select “enclosure” from the pull-down menu.

I see the Custom Fields, but it’s a free form text area, not a drop down. Is there a PlugIn that you’re using for adding the enclosure via a Custom Field?

Sorry, I answered my own question by changing the Options for Writing Posts to use Advanced Controls. However, how do you actually use the Custom Field.

I am choosing Enclosure from the Drop Down and pasting my enclosure tag info (from Libsyn) in to the Value area, but my RSS still doesn’t include the enclosure info. How would it know to apply to the link to a podcast for example? Thanks!