the leg lower sections 14a in proximity to the leg lower ends 12a an annular tub support ring 28 comprises an angle section member with a lower flange 30 having a generally horizontal orientation and outer and inner edges 32a 32b tub capture means comprising an inner generally vertical flange 34 includes a lower edge 36a and an upper free edge 36b the lower flange inner edge 32b is connected e g welded to the inner flange lower edge 36a the inner flange upper edge 36b is positioned in spaced relation inwardly from the frame assembly legs 10 each web bar 18 includes a respective retainer pin receiver 38 a plurality of retainer pins 40 e g three are shown corresponding to the number of web bars 18 are provided in the web bars 18 in proximity to respective outer ends 19a thereof each retainer pin 40 has a generally tubular configuration with a hollow bore 42 and a sidewall 44 with a longitudinal slit 46 therein the retainer pin is compressible slightly by closing the sidewall 44 on the longitudinal slit 46 and has an extended position as shown on the left side of fig2 and an inserted position as shown on the right side of fig2 since the frame assembly 4 is adapted to nest with another similar frame assembly the retainer pin 40 can be retained in position by driving it into the retainer pin receiver 38 e g with.