VanRennselaer Barnum is said to have gone west with his brother Charles. It appears likely that he was named for Colonel Van Rennselaer, who commanded the 4th NY Regiment during the Revolutionary War.
For some unknown reason, he appears in the 1850 US Census for Monguagon, Wayne County, Michigan as S. B. Barnum, as follows:
Dwelling #173; Family #173
S. B. Barnum, 40, M, Farmer, b. New York
Charity Barnum, 26, F, b. New York
Warren Barnum, 5, M, b. New York
Mary Barnum, 4, F, b. Michigan
His father Roger and brother Charles were living next door.