With similar respect to Julian, I don't see why the use of blu-tack is silly.
I explained my reasoning in my original post and as I said, none of the six plates (which I also made myself) on my loco have fallen off in five years of regular use.
As an aside, our ceramic house number tile has been fixed to the outside wall using blu-tack facing the prevailing wind and weather for 17 years and it hasn't fallen off yet.
As Mike says, he is a novice builder like myself, so I offered a practical, simple and effective solution to his problem. He doesn't have to take my advice, that is entirely up to him but it works for me.
Regards
NickM