The present invention relates to improved base for a large, commercial rooftop air conditioning (A/C) unit. The base is assembled from a series of interconnectable, corrugated floor panels having smooth bottom planar surfaces that may directly be mounted atop existing rooftop A/C unit curbs. The panels are each constructed from metal or steel, concave formed linear members that reside coplanar and are separated by a foam core. There is a base to wall panel connecting rail that simplifies the attachment of the A/c unit's side walls.
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