Always do this as the Ambers casings seem to be bullet proof.
on one of mine I actually had to ore it a little bit before it would eeven think of letting a screw in.
Bore a little, pop in a screw sometimes need to thread em in and out a few times to get a complete fit, then mount on case.
might be easier with the rubber pull thru mounts if yer usin ambers and cba to mess around.