A ferret's not bad. They're small and manageable like cats, but as interactive as dogs.
However, I have heard they have a distinctive and potent odour, that's not necessarily pleasant.
They're also inquisitive, and good at crawling through confined spaces. So I don't know if it would be risky to have one if you live in a trailer. I don't know if it would be easy for them to get outside or not, and you've already suggested you have the dangers of coyotes and birds of prey, so I think they might be at risk there.
A lizard isn't a bad idea. You keep them in a cage still (although they can come out), but being cold-blooded and slower to move, they're happy in a more confined space because they don't need to travel much.
A bird, such as a budgie isn't a bad idea. They're very very sociable, but often need to be in pairs, because otherwise they can get very lonely. But they're also smart and you can train them to say things.
As far as I know, it's not common practice to let them outside. And they're usually quite content with just a small fly about every now and then in whatever size house you have.
The downside to them is that they can be messy, and sometimes noisy.
You mentioned a dog, but were mostly worried about them injuring someone.
You can get very good tempered dogs, or simply choose a smaller dog, perhaps a toy breed or lapdog, rather than the likes of a German Shepherd, Labrador, Retriever, Rottweiler, etc...
Beagles, roosterers, Springers, Jack Russels, Terriers and similar are decent sized dogs that are usually of sound temperment (although Jack Russels can be a bit precocious/yappy without proper training). Avoid things like Chihuahua's, for while they're small, they can be fairly aggressive or boisterous.
