Depends on how they did the electrical install.
Grounding to the electrical ground is not the correct way.
If I recall my NEC correctly and how it applies to mobile homes, there should be a ground rod nearby. The trailer frame should be grounded to that, as well as the electrical ground.
Ideally, installing a new ground rod for your antenna and bonding that to the existing ground rod would be the way to go.
If the trailer is set up with just a temporary power cord, you might need to get a professional involved.
Off the record, if it was me in this situation, I'd probably drive a new 8 foot ground rod, bond that to the trailer frame and my antenna. But like I said, off the record...