I need to replace the grabrail on the cabin top exterior of my O-28. It's the straight board type, approx 1" x 1" x 80", as opposed to the traditional sectioned grabrail type. Can someone tell me how it is screwed on? I can see that there are dowel plugs covering the screws, but I don't know what the screws are screwed into. I can't locate any nuts or nut covers on the inside. Is it possible that the screws are screwed into the interior grabrail on the cabin roof?