According to The Telegraph, JR Hildebrant's vessel contains enough room for a chair, a small propane heater and himself.
"The smell may get bad for a while," he confessed.
The journey, which is expected to take eight days, aims to raise money for a charity that sends children with special needs to destinations such as Disneyland.
In previous years, Hildebrant has won Wisconsin's Nekoosa Great Pumpkin Race, taking ten minutes to complete the 300-yard course.
John Flodstrom, who will help tow the boat at various stopping points along the river, said of his colleague: "I thought he was crazy. I give him a lot of credit for what he's doing but I'm glad he's in the pumpkin and not me."