I think you can at least put the model in for MP. You would just have to find where it is. But you woudnt be able to pick up a weapon from it. You could try doing something like putting a weapon pickup behind the wall where the rack is, far enough that you cant see the pickup (or at least most of it) but close enough so that its pickup radius sticks out past the wall. So that way when the player goes up against the wall where the gun rack is, they pick up whatever gun you put behind the wall.