I have experienced the same thing with multiple Airstreams. The way I have fixed them in the past is to drill new holes the frame of the bed and attach it to the skin in new places. I have noticed that the couches are usually not attached to the ribs. I do not know why. I have reattached using the same screws and usually try to get one rib near each end for strength. If the holes bother you could fill them with oversized Aluminum rivets.
I do not drill through the skin; I allow the screw to make its own hole. This is for other than the rib mount. There I drill a hole in the rib smaller than the screw to get a good bite. I would be afraid to try to force the screw into a rib. To make the job really easy you could use self tapping screw of the same size as the ones you took out.