Hi, I see you have no responses so far and while I am not familiar with your coach, it is not unusual to have screws undo themselves from certain vibration patterns over time. I have seen floor screws with lino on top undo themselves up under the floor. So the question is did the screws just rotate down or did they “pull out” of the support material in the ceiling from too much weight? In other words can you tighten them up again and are they holding tight? If they were going into metal supports you could try using blue locktite thread locker on the exposed screw threads and tighten them up.......but if they are going into (or through) wood support I don't think thread locker is appropriate. In that case you could try lock washers and a flat head style screw with flat washer below to try to prevent screw rotation from vibration. At least that way you can remove the screws in future if required.......blue locktite also allows removal as well but probably not the best in this case.
The sheer weight of the cabinet just pulled the screws out from under the over-the-cab bunk from vibration. You can have the best workmanship available, but if the materials used are inferior then this is the result. Cabinates falling during normal use.