I think for Helm's version is
Capo 2nd fret:
Em    -    B7 (or B - I use B7 for more bluesy sound)
(x4) all the verses
(x3) third, sixth and eighth verse
In the last rhyme of the third, sixth and eighth verse we got
Em - G - A - B7 - D - B7 - Em

Sorry I type it this way but I think you'll understand