Tracing a short

First of all, which breaker is it? Which circuit does it control?

FYI a breaker doesn't blow a fuse. A breaker "trips" when it sees more current flowing through it than it's rated for. Fuses "blow" when they see more current then they're rated for. So breakers and fuses perform the same function, the difference being that a breaker can be reset while a fuse has to be replaced.

So, you have a short or overload somewhere that is tripping a breaker in your 120Vac system. That means that you are either "chasing a spark" or looking for a load device that is taking too much current.

Since you don't want to be a spark chaser, my recommendation is that if you can't find a load device that's overloading the circuit (should be obvious) that you take your trailer to a shop for repairs. Chasing down shorts can be hazardous.