OP
jase31
if you use a fastfix box ..when you offer up the base...it will have the effect of "trapping" the box between the plaster and the base....your fixing the base to the plaster ceiling...not the box arnt you?.........so all you are creating is a "cavity" within the box for terminations......
Yep, the detector ceiling plate will hold the box against the ceiling, just need to cut a square hole in with fein, and secure with the alarm ceiling plate.