This is an update to address randomspawns not happening. Replace the value in the world: section of the randomspawn/PortableArenaRandomSpawns file to allow spawning of the arenas randomly in your worlds. Make sure to paste the new PortableArenaRandomSpawns to replace the old one. THE OLD ONE DID NOT WORK! This one does.
Keep in mind the make sure the spawn rate is set incredibly low. If you increase it over .01 you will flood your server with entities.Your players will crash. BE CAREFUL! I have found a setting of .00001 keeps the spawn rate in the "rare" category. .0001 will still create quite a lot of arenas for a player that is online for a long time.