In reality there are very few screws attaching the actual wall panels to the van metal walls (top & bottom). The walls are attached to the back of the cabinets with L-brackets or via the window boxes. The cabinets are securely attached thru the floor.
"Cabinet sides are bolted down through the van’s steel floor using 8 to 12 special steel “L” plates. Cabinets are also secured to the van’s sides, and other appropriate points.
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-greg
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