My wife's cat will alert us when we have one, but the dang thing won't go after them. Isn't interested in them even when she sees one! You might try some of the block poison. I've used the little nuggets on our hunting property, but they will collect them in a stash before it gets them. The theory with mouse poison it they'll eat it, then get super thirsty, and go outside to a water source. However sometimes they don't make it, then you've got the smell for awhile. You might try mothballs maybe it'll run them out.
As far as them getting in, they have to get in somewhere that your rig has contact with the ground. When we were getting them, I'm thinking that they were climbing the front jacks, as when I started putting traps in the front basement, I'd catch at least one a day, & wouldn't have them in the coach. We were work camping at the time, & I didn't do anything until we got home, then I went around and filled every hole I could find with the spray foam, and we haven't had any since then. One thing we started doing after that is that we heard that putting white rope lights all around the camper, & leaving them on 24/7 would keep them away. Don't know if it was filling the holes with foam, or the rope lights, or both, but we haven't had a mouse since.