That is wicked cool. thanks for the underside picture. I've never seen those before again thank you.
I forget the U.S. is the not the only place these cars were sold - sorry for my narrow minded view.
I again would assume the standard mirror gasket would work- or a closed cell black foam like 1/8" or 3.175mm thick-ish.
Trim to fit a slightly larger than base of plate for a proper look.
