Conversion vehicle shipments in September dropped 19.4 percent compared with the same month last year.
A total of 5,000 units were shipped.
Van conversions, which accounted for the largest portion of conversion shipments, fell 19.0 percent to 3,400 units.
Pickup conversions fell 12.5 percent to 1,400 units.
SUV conversions took the largest percentage drop, down 50 percent to 200 units.
Conversion shipments for the first nine months of the year were down 12.5 percent.
Motor home shipments remained flat in September at 5,700 units.
Class As, which represent most of the motor home segment, were up 2.7 percent to 3,800 units.
Class Bs fell 33.3 percent to 200 units. Class Cs were unchanged at 1,700 units.
Motor home shipments for the first nine months of the year were down 0.7 percent.