Apply glue at each end on the bottom sides of the attached slats. Flip the leg and trestle assembly and position it flush with the aprons so that it rests on the glue of the two slatted bottoms. The aprons should extend 1-1/2" beyond the legs at each end of the bench. Drive 2-1/2" deck screws through the braces and into both slats.
Position the middle brace between the aprons, centered end-to-end on the project. Fasten it to the two side slats with deck screws. Position the six remaining slats on the braces using 1/2"-thick spacers to create equal gaps between them. Attach the slats with glue and drive 2-1/2" deck screws up through the braces and into each slat (photo 6).