by a plurality of spaces 25 this arrangement is not described in detail in this application because it is the subject of a copending application ser no 121 031 filed nov 16 1987 in the name of inventors joseph j hart david j c glasgow and richard w carpenter still referring to fig3 and 4 it will be seen that the center of panel 10 is supported by a structure that includes a pair of first and second support panels 30 and 40 which are formed from material cut from center panel 10 and foldably joined therto along intersecting fold lines 31 and 41 respectively that preferably extend in directions normal to each other first support panel 30 includes an opening 33 having first and second portions or areas 33a and 33b respectively support panel 30 also includes an abutment or projection 34 extending into opening 33 between the separate areas of the opening area 33b may be provided with a curved edge 36 to facilitate folding the second support panel 40 into interlocking engagement with the first support panel 30 as hereinafter described second support panel 40 includes first and second sections 40a and 40b respectively which are separated from each other by an opening 43 opening 43 is relatively small and narrows to a only a slit at the edge of the panel so the abutting ends 46 of the respective panel sections 40a and 40b will engage opposite sides of.