I have a OPTIONAL EQUIPMENT AND ACCESSORIES PRICE LIST from Denney Aerocraft circa 1989 in my files. It shows two underbelly cargo options:
Cargo Pod, fiberglass, looks like a drop tank . . . 289.00
(Hangs between the landing gear, detaches quickly)
Cargo Container, 5.3 ft.3 capacity, huge! . . . ... . 420.00
(Fiberglass, hangs under fuselage center section tight against belly like on a Cessna Caravan. Has two hinged doors. Removable with 4 bolts, weighs approximately 25lbs., requires mounting brackets and special truss welded to fuselage.)