A quiet gem of a story, beautifully awkward in the best and most real of senses. You've perfectly captured what I imagine to be the dynamic between the Marauders and Peter. I love watching Peter's slow and subtle development here, as he gradually learns to value himself apart from his friends. That it's Mundungus who leads him in this journey makes good sense -- it has to be someone like Dung, another misfit, but one who has the confidence that Peter lacks.
My favorite part of the story is that wonderfully awkward conversation in the little cleft cottage (and what a perfect Mundungus rationale for the place) -- it's a scene that is touching, moving, and excruciating at the same time.
Mundungus didn't look like a bloke who sat about the place reading poems to himself anyway. Haha! Well, yes, and no. This story is its own sort of poem.