The holes for the bumpers, posts etc are cut after the mylar has been applied (not yet done in these pics). After the mylar is on, i then burnish it down hard by rubbing it down using the back of a table spoon, before the protective film is removed from the mylar. After its burnished down i then remove the protective film, revealing nice shiny mylar!!

I usually cut out all the post / bumper holes etc after the burnishing step.