John I might not be understanding, “…the other two mounting points go from underneath.”
The Tech Tip appears to correctly show the rear mounting assembly sequence in the third drawing. The two bolts pass horizontally through a mounting wood block and held in place with washers and nuts. The long carriage bolt, offset washer passes through the bed board and the wood mounting block and frame rail and held in place with a washer and nut. That sequence is completed under the bed. That is the way Sparky’s bed was assembled and as described in the bed kit instructions Mar-K provided, as I recall.
The attached photo shows the two bolt heads on the rear of the bed outside.
