As it turned out, there was almost nothing inside the wood channel. Water lines from sinks were inside it for a few inches, right next to the outside wall, but they went down to the grey water tank almost immediately. I injured nothing cutting out a section nearer the toilet to get the riser to fit. Of course after I reinstalled everything, the water valve at the rear of the toilet started leaking so I removed the toilet again, installed a new valve, reinstalled toilet and all is well.
Jim McPheters
08 Dip 40 pdq