I'm a pro at this.
Powerdrill + expensive hard drill bit + lock cylinder = busted. I used to break a lot of masters. Get a drill bit that's about 1/3 the size of the cylinder and go at it. It takes about 30 minutes, but it's better than paying $100 to a locksmith. Since it's on the trailer it will be a pain to hold onto and drill at the same time, just be really careful. I used to put the locks in a vice so I didn't have to worry about that. The only problem is that the whole lock will get burning hot...get an oven mitt..
Another option is the car jack method, if you have one strong enough and the lock is low enough to the ground. Just drape a towel over the lock once you have the jack set tight under it...the lock is going to go flying when it breaks. This is probably not a good idea if the lock is mounted to something weaker than it, because it will tear off whatever it is attached to before the lock breaks.
A hacksaw will work, and it's usually the quickest way. Wrap a lot of electrical tape around one side of the loop, about a millimeter away from where the loop goes into the lock. This will be your guide for the saw. Take the blade and saw through a bar of soap to lube the blade, then start cutting. You can get through the lock in about 5 minutes. You just have to make sure you cut the side that isn't attached to the lock. Once you cut the right side, the other side will spin open. If you cut the wrong side...sometimes nothing happens and you have to do the other side.
60% of the time, it works every time.