Since you are asking about common usage, I'll give an answer in that perspective.
I've never once heard, nor ever heard any of my friends, family or associates, use the word "trousers" when being serious.
It just sounds old-fashioned in this country, or of course, British.
The only time I've heard someone say "trousers" would be when they are either imitating a British accent or talking about a different time.
Mind you, this is my Midwestern, AmE opinion; it's only that. I've lived all over the Midwest, East Coast and South. I can't attest much to the wording that people to the West use. They are often quite different.
