I was looking at this post by Ivan Dimitrov and his suggestion to the original question.
I have a very similar requirement wherein, on the edit of UserControl i need to get TextArea(RadEditor control) for one of the properties.
When I try to create the custom Webeditor class in the App_code, I get the error on the line: Telerik.Cms.Web.UI.Control.WebUITypeEditor<string>
It says cms does not exist in the namespace. Could you please suggest the alternative for this?