It had been a while since I read Ghost Story, but as I remember it, the only time Harry describes
Bob with a body, is when he is inside Bob's scull and goes on to also describe the living quarters inside the scull. Not unlike DR Who's Tardis seems to be bigger on the inside than the outside or the scull that we see like the Police Box. I remember Evil Bob running around, but I cannot remember beyond that. However I think that was on a different plane of existence, allowing for Evil Bob to have a body.. Or since he is Evil Bob, he can chose to break the rules that normally define Bob's existence. Otherwise outside of his scull, Bob doesn't have a body, when Harry has given him leave or asked him to explore, he usually has to do it with Mister as a car, he can't just go on his own. In the chase in Skin Game, Bob is still in his scull in a special pack that Butters invented.