I took the pieces apart to show more detail.
"Exploded View", Half way position
The bottom piece is a Drawer Glide, like for a kitchen cabinet. There are 2 pairs of glides.
It attaches to the lip around the body's opening.
It's 23 inches long and about 1-1/4 inch high
The center arm has opposing curves on both long sides. Each end is cut and drilled to match.
One way is for the left side, and flip it over for the right side.
The angle connects to the roof section. The single bottom bolt attaches to the center arm. The 2 top bolts attach through holes in the roof. They are a common leak point.
It's actually 6 inches long by about 1-1/4 inch