When it’s impossible to back the end joints of drywall on a ceiling, I use a batten of drywall about 6 in. wide, as shown. I screw through both layers with drywall screws, and secure the screws with heavy-duty insect screen. When the sharp screw tip hits the insect screen it finds the nearest void in the weave, spreading the strands apart until the shank can pass through the screen. The threads bear on the wire strands, giving me a solid purchase for the screws.
Robert L Kennedy, Grand Forks, ND