Well it sounds like quite a problem you have there. Are you able to get to the area from near a ceiling vent? You could loosen the ceiling around the vent and pull it down. I have to admit, we don't have any 70's trailers but pre 1967
you can drill the pop rivits out and the ceiling will drop but you have the upper cabinets to deal with also. I don't see any quick way to deal with your problem. Ideally you would like to repair without cutting so interior removal in that area may be necessary. In the older trailers the ceiling is usually 2-3 pieces of aluminum buck rivited together to form one piece. Hope this helps in some small way. Keep us posted.