As with most repellents, they make the local environment less appealing to the rodent. That's a good thing in the sense that if the rodent can find something better, they'll move on. But it's not a sure bet. If your trailer, even with the repellent, is the best they can find then they'll put up with the noise. (Keeping warm in the winter is a high priority.) YMMV.
Ultrasonic sound is blocked by pretty much any physical object (wall, bench, table, etc ...).
2014 Innsbruck Lite 198BH