User control inheritence

I have a business need to design two types of user controls. So, the hierarchy I have is something like this:
 
                 Base User Control
 
Type1Base                      Type2Base
 
Type1Instance1              Type2Instance1
 
The base user control will be a regular .cs file inheriting from System.Web.UserControl. The Type1Instance1 and Typ2Instance1 are .ascx.cs files inheriting from Type1Base and Type2Base.
Now, what are the pros and cons of making Type1Base a .ascx.cs file over .cs file? I know .ascx.cs will give me designer support. At this point, i think there will be no UI controls at the Type1Base level.
 Any thoughts on a good design?

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