The splitter box is a plastic box used by electricity companies to house outdoors connectors, fuse boxes or power meters.
The box is constructed from white plastic and should be impenetrable to water. To be on a safe side, I have included few small drainage holes at bottom and sealed wall and top connections with silicone.
Inside the box, a water-resistant plywood panel is attached - it forms a mounting base for accessories which will be permanently mounted inside - 12 power connectors, 230V power splitter, USB active hub, Robofocus and FLI DF-2 controllers.
The box is attached to the balcony railing with a set of aluminum tubes - which I have covered with heat shrink tubing to prevent marring the paint on the railing. The attaching bolts and nuts are stainless steel.