One near me is having an issue with rats. I think really they just need better trash pickup mainly, and better shelters in general, but they've specifically asked for help getting rat poison. Would bait boxes with poison even make a dent in an outdoor environment like that? I can't singlehandedly improve the cleanliness of the camp or get everyone rat-proof shelter obviously, but I feel like just going straight for the poison could have adverse consequences and not be effective, potentially.
Rat poison will definitely bring the numbers down. I don't touch the stuff but I don't live in a city so I worry about secondary poisoning. You'll never get rid of all the rats until there is nothing to eat and nowhere to live but poison can keep them to manageable levels but you have to keep it up.