Warning with Inheriting from a Class that Inherits bpy.types.Panel

Here’s a few threads that might help:

It seems like it is possible, though it doesn’t necessarily work exactly how you expect.
Instead of creating a custom panel that inherits from a predefined panel they want you to create an abstract class with all your custom info, then create a standard panel that inherits from your abstract class and bpy.types.Panel.
From one of the links (though others suggest putting the mixin class before the Blender class):

class CommonProps:
    s = StringProperty(name="s",default="ABC")

class Base(bpy.types.PropertyGroup, CommonProps):
    pass

class Child(bpy.types.PropertyGroup, CommonProps):
    pass