What is your power supply and how big is the ventilation fan?
If it's an older electrical system with a 30amp outlet and it's a big exhaust fan, you might be popping the breaker all the time.
A big fan that will really keep the attic temps down might pull 5-6amps (plus whatever else you have running in the trailer. A smaller fan will pull less but won't keep it as cool. On startup, the air/con will likely be within a few amps of popping the breaker to start with, so it's a question of if you have enough amps to get everything going.
Once going, it will likely work but it's a question of startup loads. This is a common discussion in relation to small generators running air/con but you might run into it.
