I have updated the bridge and the trap door parts. The new bridge doesn't let dice jump out so easily, but they still can if you drop them from above the tower.
Thanks to the makers (FluffyB and RaunoProps) who gave input for improving this.
Thanks to 3E8 for suggesting the under stairs hole expansion. I probably wouldn't have tried it otherwise.
Pu1p made a flagpole for the secret door switch. Check it out: http://www.thingiverse.com/thing:2043609