Bill,
Different year and model coaches require different items to be removed or disconnected to gain access to the the plumbing that is behind the panel in the plumbing bay. It will not be difficult to remove the panel, however it will be tedious and time consuming on most coaches. The knobs just pull off on most coaches, however the manifold for the valves that the knobs control are usually bolted to the panel. So you will probably have to remove the attaching screws for the manifolds and disconnect the water lines to the outside shower and city water fill to gain access.
Gerald