All circuit breakers and fuses trip/blow when they get too hot. That's the way they're designed to work--as a "weak point" in the circuit that protects the wiring in the rest of the circuit. Too much current is why they get hot.
So, what's pulling too much current? Possible culprits include, but are not limited to:
1. Low voltage--what kind of supply is your trailer plugged into? Running an air conditioner needs an honest 30 amps of 120 volt power. Sometimes the campground has skimped on their wiring, and the voltage drops when everyone turns on their AC.
2. Shorted circuit--is one of the wires rubbing something so the insulation is bad and the conductor is touching metal?
3. Dirty, corroded, or loose connections--increases resistance in the circuit and that pulls more current.
4. Bad component--is the air conditioner itself going bad?
5. Old, tired circuit breaker--these things get a little weaker with age and also with each time they trip.
For some reason, my personal troubleshooting philosophy is to start with the cheapest alternative first. Of course, do only what you can do safely and hire an expert for the rest.