Composite doors for transport refrigeration unit

The front cover of a transport refrigeration unit includes a plurality of hinged access doors, with each door being formed of a pair of spaced thermoplastic olefin sheets with their edges being bonded along the entire periphery of the door to form a hollow space between the sheets without a need for foam. The edges are bonded by a thermoforming process which provides strength and rigidity to the door. Additional thermoforming bonds are made at locations other than the periphery to provide further strength and rigidity. A ribbing structure is formed in one of the sheets and extends around the periphery thereof. Further ribbing may extend transversely across the sheet in non-peripheral positions.