The above 1850 lithograph is a somewhat fanciful depiction of Brown's unpacking; that's Frederick Douglass to the left. (No, I don't know why the man on the right is holding a picnic basket.) Suddenly famous, Henry "Box" Brown became a spokesperson for the abolitionist movement, and as the Library of Congress notes, "The box itself became an abolitionist metaphor for the inhumanity and spiritual suffocation of slavery."
Fearful of professional slave hunters, Brown traveled to England and put on exhibitions and and magic shows where he was mailed from one performance to the next. (The act would begin with him being unpacked from a crate.) This theme was so popular, Brown added an act where he escaped from a suspended canvas bag wrapped with a padlocked chain. (Decades later, a Hungarian immigrant to the U.S. whose stage-name was Houdini took escapism to new heights.)
My sources are here.