Most brands of trail running shoes are only offered in medium widths, and this makes fitting a narrow foot extremely difficult. Asics GT-2000 and Brooks Adrenaline ASR are my current favorites in this category, offering medium width trail running shoes which run narrow.
Both brands are excellent in terms of design and support. However Asics GT-2000 takes a slight lead in the narrow-shallow department, whereas Brooks takes a slight lead in the support department.
An added bonus — both brands offer Gore-Tex, waterproof versions of the above models.