I work in the car parts air transport business myself, and have frequently seen this aircraft in Laredo. Cargo flying lends itself to older airplanes because new ones are so expensive. Unless your profit margin compares to Fedex, it’s awfully hard to pay those prices. Flying car parts has a very high profit per trip, but it’s all unscheduled, with no guarantees of a steady cash flow. You don’t want an expensive asset sitting around doing nothing half the time. In the case of the Convair, I would guess it was just the owners hobby, rather than a serious business.