Abstract: A monolithic bathtub structure incorporates vertical support columns that in one aspect are integral with the bathtub and which can be secured directly to the stud framing of the cubicle in which the bathtub is installed. The bathtub structure includes a suspension beam incorporating a locking mechanism to prevent inadvertent release of the access panels from the assembly, yet the locking mechanism may be adjusted to permit removal of the access panels. In other aspects of the invention, the suspension beam, including the panel locking mechanism, and the support columns may be independently manufactured as component parts to be assembled by the purchaser to form a bathtub enclosure. The monolithic bathtub structure is capable of formation from an appropriate synthetic resinous material, as are the support columns.