The application provides unique assembly, shipping, display, nesting and compact stowing methods for compact or convertible nullsub-assembliesnull for wheelbarrow and cart devices. The wheelbarrow or carrier device nullsub-assemblynull comprising all or some of the interconnected component parts of the device (except for the tub or base) may be selectively movable and stowable to the inside or underside of the cargo carrier, with the user only being required to move and rapidly secure the sub-assembly frame to the device. The wheelbarrow or cart nullsub-assemblynull disclosed may be entirely or substantially stowed within the side elevational profile and interior of the carrier device carrier space during shipping, transport or sales display, and/or selectively attached to the underside of the base or tub for shipping or display prior to actual use, by a series of any suitable quick release methods commonly known in the art. Other novel component parts of the said sub-assembly units for wheelbarrow or cart devices are also disclosed, including convertible methods allowing the carrier device to be either hitch mounted or trailer connected to a separate wheeled device, allowing the carrier to be mounted in either a setup or a stowed condition.