My '68 had a 1 X 2 piece of wood under the front part of the shelf which was
screwed to the trailer. It only ran the flat part of the trailer. The
shelf was screwed to the board along the front part of the trailer. The
shelf itself was made of a piece of plywood and a 1X2 rear edge (facing the
rear of the trailer). The 1X2 had a groove cut in it for the plywood to
fit into. At each end of the shelf it was screwed to the trailer which gave
it the stiffness around the corners. Please contact me off list if you want
some pictures. Easy to see the construction with the couch down.
Pete