Same problem with the suction cups. We mounted the soap dish down low at the corner above the tub. The tub holds it in place.
We used to use the suction hooks that mounted to the wall, but they won't stick. We begun using clips with a magnet on the side of the range hood, etc. Anywhere it could find a metallic surface.
I also bought four of the hooks that pull down and have aspring that makes them retract into the holder (chrome). I mounted them on the side wall of the refrigerator near the side exit door of the 235. There is a small ledge above the refrigerator that they mounted on quite well. I don't recall the floor plan of the 225.