May I suggest listening to any field recordings first, many of us don't but it does help in understanding the song before you listen & get it from others. It's always nice to be one step away from the field when first learning a song rather than a few miles it's starting point.

While at the Getaway I just picked up from Camsco (Thanks Dick & Susan) volumes 1 & 2 of the Gardner Collection on Folktrax (141 &142). There are 4 versions of Shallow Brown (short clips actually) on vol 2. The recordings are from the field tapes & a bit rough but I'd say if you are gonna bother to learn a version don't until you've given a listen to the originals as they were sung by those that actually had to work with them under sail, at least not if you can get the chance & can, it may change the way you want to sing & present the song & it would certinally be an aid in digesting & swallowing the song before you bring it back up & out (what a nice visual??).
Good luck, it's a beautiful song

Barry