I would paint it grey, or metal grey, This is available as interior paint (pending which sub your trying to reflect). then use PVC piping also painted grey. Its Light weight, can be attached to the walls, and can be placed in a manner to look functional. And there are different sizes and valves available for it, so it can show water piping to wire routing. There is decorative house trim, I think its like a plastic, can be cut to fit to show internal structure build. Then Something like a fuse box, but it it just looks like one, it plugs into the main house power, and anything inside will work off this. Example; If you work off one outlet with a surge switch board and a extension cord, then the fuse box will only have one socket and one plug to the wall, no different than a extension cord just more decorative... Then the main lay out build such as monitors and controls, very much like what you got going on after I had set up the "sub build" look. That is what I am thinking on..
