Tim,
I notice you have all of your extra numbers stacked up beneath the ones showing......Is that the way they were supposed to be? Not that worried about original, but I do have a pile of numbers just laying on a shelf now!
I just used my "0" and "4" and then dropped the combination plate on top, "C" facing backward of course, because I don't have a trailer. Works fine and there's enough tension to keep the top plate from moving backward off the lugs.
"Free advice is worth what you pay for it."™