these rows and columns are offset lateral rows 34 or offset longitudinal columns 36 from one another this arrangement of offset lateral rows 34 and offset longitudinal columns 36 forms a jigsaw like circumferential profile of the outer perimeter sidewall 6 by offsetting a lateral row of grid sections 24 by one grid section a profile in the sidewall 6 is created having at least a recess 40 on one side of the support grid 1 and a protruding grid square 42 defining the sidewall on the opposing side of the support grid i e on the other end of the respective lateral row similarly one or more offset longitudinal columns 36 of grid sections 24 could be offset from the other columns 32 so that a recess 41 is formed in one end of the support grid 1 and a protruding grid square 43 extends at the opposite end of the support grid 1 from the recess it is also to be appreciated that the offset rows and columns 34 36 do not have to be offset as described above or offset by a complete grid square 24 it could be that certain rows and columns may define a recess 40 41 by providing one less grid section or a smaller.