A wall panel assembly for a heating, ventilation, and air conditioning (HVAC) unit includes a panel having a main body, where the panel is configured to be fastened to a frame of the HVAC unit, and a plurality of stiffeners attached to the panel along a perimeter of the main body. A stiffener of the plurality of stiffeners includes a flat portion and a raised portion offset from the flat portion, where the raised portion is configured to sealingly engage with a component disposed within the HVAC unit.