I have to build a box to extend the length of a projector bracket:
The projector bracket weighs 7kg and has an arm of about 500mm. The projector weighs another 5kg.
The box has a depth of 140mm. That is the length by which I need to extend the length of the projector arm because the wall on which the bracket is mounted is recessed by 140mm behind the image surface.
Does one of the following two ways of joining offer a stronger structure?
I don't have tools to make complex joints. I can only screw ½" plywood at right angles.