As to where trailers were played "in the good old days" (at least in the US) it's not exactly accurate to say that they ran after the movie...
Well, I'm in Australia, so I was speaking from my experience. Trailers trailed
either the first feature or the introductory short, which is how they came to be called trailers.
By 1979, double features were religated to suburban and regional cinemas Down Under. I don't recall whether there was a short with TMP, but ST II came with "Rockinghorse Winner". Snore!