A different way of securing our transparent plastic box
The reason why we used cable tie to secure the plastic box to the L bracket is to allow a slight freedom of movement of the L bracket to be adjusted so that the bottom of the L bracket will lie flat on the acrylic surface of the vessel.
If we instead used a nut and bolt to secure the L bracket to the plastic container, the bottom of the L bracket will not lie flat on the acrylic surface as the sides of the plastic container is not 90 degrees perpendicular to the plastic container.