I did like this for Collection inside UserControl:

1. Create myUserControl.ascx
    ...
Private oCol as New Collection
    ...
Public ReadOnly Property PathList() as Collection
      Get 
          Return oCol
      End Get
End Property

2. Declare and create new instance of UserControl.ascx in WebForm.aspx

   Dim myList as myUserControl = Page.LoadControl("")
       myList.PathList.Add("c:\folder")
   ....

3.   It's working for me..