preferred knockdown boom 30 includes a pair of elongated boom legs 32 and 34 the lower ends of the two legs are pivotally connected to the truck bed 14 adjacent sidewalls 16 and 18 and tailgate 26 each of the legs has a generally tubular construction the lower leg ends are mounted on foot structures that include structural angles 40 and 98 respectively the structural angles are identical to one another except for a right and left hand relationship structural angle 40 is illustrated in greater detail in fig4 structural angle 40 is mounted on truck bed 14 as in fig2 and 5 angle 40 has a horizontal wall 42 having a pair of fastener receiving openings 44 and 46 fastener means 48 and 50 are passed through openings 44 and 46 respectively and through an aligned pair of openings 47 and 49 in the truck bed a plate 52 is mounted beneath truck bed 14 between support members of the bed not shown so that the truck bed is sandwiched between plate 52 and structural angle 40 plate 52 has a pair of openings 54 and 56 for receiving fastener means 50 and 48 respectively for fastening the plate and the structural angle to the truck bed plate 52 has openings 58 and 60 for receiving fasteners 62 and 64.