I don't have the same model but looking at the floor plan and specs, it is highly likely what you are feeling the underbelly up against is the kitchen sink gray tank. Either pull some shot pins to peak in there to confirm, OR, empty your kitchen gray tank and push up on the underbelly at this location and see if it now pushes up more without as much water in the tank. It is actually pretty crazy how much the holding tanks deform when full. They really sag down in the middle of the tank.