Yes, that trick ought to work! I verified that your code works with a slightly modified XAML (I used SilverLight 4):

StackPanels size to the size of the content. In your case, the size is 0x0, so you don't see anything. You need to have your d namespace defined in the my:UDW_Details XAML and then add: d:DesignWidth="300" d:DesignHeight="300" to have a design time width and height. or you can stub in design time data. Either way works.