Dudley's thoughts are expressed in such perfect IC language; I like your version of him tremendously, and yet he fits his canon depiction, too. It makes perfect sense that his experiences with the wizarding world would have strongly marked him, for better (doesn't want to make people afraid) and worse (shame and panic attacks). Some great lines:
For all Dudley knew, that lot only got together for the annual blood sacrifice and dinner dance and nothing more.
Perhaps she was some sort of demented singing telegram girl?
It hacked him off that he couldn't even watch a bit of mindless telly without being reminded of the utter humiliation and trauma those nutters had caused. Very believable.
Dudley had never heard of The Quibbler, but he wasn't much of a reader, and it sounded like some sort of girly thing they sold in the cosmetic section of Boots.