Here's a reference to singing of Black cotton-stowers in Savannah, in a letter from 1818. No detail, just that,

No business being done in Savannah during the summer, or sickly months, it is now all activity; nothing is heard near the water but the negroes' song while stowing away the cotton...

REMARKS MADE DURING A TOUR THROUGH THE UNITED STATES OF AMERICA...(1817-1819), published 1821, by William Tell Harris, pg. 69

So at least we know that as early as the 1810s, the singing whilst cotton-stowing was going on, albeit nothing of its form.