I used to poison them. It worked well. I found a big rat dead in the back yard tangled in some vines. They generally do leave after being poisoned.
Then one day I began smelling a dead rat inside the trailer. I looked everywhere for it, but no luck. I suffered the smell for months. It gradually dissipated, but every time I turned on the air conditioner, there it was again. Finally the smell went away, at long last!
Years later, I was doing some renovation inside the trailer and pulled back some insulation and there it was, a big rat skeleton.
Nowadays, I use traditional spring traps with peanut butter. They work well.