Abstract: A modular frame and system for supporting a swim spa, hot tub, or other water containment vessel is contemplated. The system includes a plurality of keyed vertical members attachable to cooperating grooves in horizontal rails. The ends of the horizontal rails attach via keyed projections to a corner bracket, while a retaining member secures to a groove in horizontal rail to secure an integrated protective bottom sheet. All of these components can be manufactured in standardized dimensions relying upon low-cost, light-weight polymeric materials. Methods and systems for using these components in a variety of customizable arrangements are also contemplated.