It all depends on the tub. If it’s a cheaper tub with a cabinet that’s not solid, and limited supports behind the cabinet, it’s probably not a good idea to mount that without taking the side off and adding more frame supports to anchor to. If it’s a solid cabinet with some supports behind that can be drilled in to, it probably doesn’t need reinforced. Those cover shelf type lifts put a lot more stress on a cabinet than a normal cover lift.