Deej,
As far as keeping the plate on (I also have had the same problem), either use sticky tape on the nut side (oooooh) or drill a small hole in the screw bit behind the plate after you have tightened them and pass a thin bit of wire through the hole. Even if the nut works loose it'll still stay on.
By the way, I also tried PTFE tape on the thread but it didn't work.
