Hi Rich,

Thanks for your post.

Based on my understanding, you want to expose an inner Panel control in the
UserControl level, so that in Form/UserControl designer, we can directly
drop another control onto this inner panel, and IDE will generate code to
add this control into Panel.Controls collection. If I misunderstand you,
please feel free to tell me, thanks

Yes, this is a design-time limitation of VS.net2003, which has finally been
added in VS2005.
In VS2005, winform designer released INestedContainer interface, which
encapsulate this function. We can just  create a new ControlDesigner, then
in its Initialize method, use ControlDesigner.EnableDesignMode to enable
this inner Panel control's design mode function.

Sample code listed below:
public class MyPanelControlDesigner: ControlDesigner
{
   public override void Initialize(IComponent c)
   {
       base.Initialize(c);
       UserControl1 ctl = (UserControl1)c;
       EnableDesignMode(ctl.MyPanel, "MyPanel");
   }
}

[Designer(typeof(MyPanelControlDesigner))]
partial class UserControl1
{
   
[DesignerSerializationVisibility(DesignerSerializationVisibility.Content)]
    public System.Windows.Forms.Panel MyPanel
    {
        get
        {
            return this.panel1;
        }
        set
        {
            this.panel1=value;
        }
    }
}
This works well on my side. Hope it helps

Best regards,
Jeffrey Tan
Microsoft Online Partner Support