I drilled and tapped the floor of the van, the steel is pretty thick and tough there, after countersinking the trim and screwing Allen head machine bolts in it is rock solid and there's nothing for the door (or me) to catch on.
Line the trim up exactly where it should be, trim comes with holes already in it, use these as a guide to drill the van floor. Can't remember size of drill used but when you buy the rivets it should say what size drill to use.