I've seen 2 kinds, the one that's just a digital antenna, and the kind that pirates movies off the internet. As mentioned above, the antenna on your trailer is probably better then the one that's a digital antenna.
The one that grabs pirated movies, tv, and such do work, more or less. From what I've heard, sometimes they work, sometimes not. Depends on usage, available network speed, and the reliability of the providers, if you want to call them such. I can't imagine it's legal, but that doesn't bother everyone.