The C-shaped piece of metal that is attached to the backside of the Stainless steel trim.
To me, seems to be the culprit as to why it so hard to install.
It wraps around or is hooked behind the backside of the glass. Picture

I've never installed the SS trim and never seen the backside of the trim.
Does the c-shaped piece of metal that is attached to the backside of the Stainless steel trim, run the length of the trim?
Or are there multiple short C-shaped pieces?