The slide floor is usually a solid piece of plywood. The underside is what you see when you stand outside. Any wires needed are usually brought along the wall, hidden in/behind whatever cabinetry is there in your layout.
My '04 Tradition had the entire tv/satellite entertainment center in the streetside slide, plus some 12v lighting, central vacuum, speaker wiring and 120v outlets. A big bundle of wires was routed from the rearward end of the slide, along the wall and behind/thru upper and lower cabinets.
Former owner of 2004 American Tradition and several other RVs
Home is in the Ocala Nat'l Forest near Ocala, FL
Summers in Black Mountain, NC