I haven't done it, and have only been in the area once, so I'm far from an authority. However, the exit at Middle Trail shouldn't be too difficult if you're into that kind of thing http://hikearizona.com/photo.php?ZIP=562812
and once out of the gulch I would think the 2-3 miles of hiking to get to the arch would be reasonably easy to accomplish while dipping in and out of the various drainages you'll have to traverse. (If off-trail desert hiking is your thing).
The main challenge would be probably be water, as you'd have to spend the night somewhere out of Buckskin Canyon or on the small slab area near Middle Trail before continuing downstream.
Edit: This wasn't linked to the post yet, so you might not have seen it: http://hikearizona.com/decoder.php?ZTN=13507