You can test my theory before replacing the switch. Unplug the trailer. Turn the switch on and then plug in the trailer. If the breaker does not trip, you need to replace the switch with one rated for motor starting.
That's sort of funny since I put the switch in to avoid just jamming the plug into the socket. I'll give this a try because quite frankly as a Manufacturing Engineer, I'd have a hard time arguing with an Ex Rocket Scientist!
Don't take the ExRocketScientist thing too far. I modelled propulsion systems in software for maneuver analysis and maneuver planning systems. That doesn't make me an expert at all things electrical. I know more than the average person on the street about household wiring -- I was an apprentice electrician for a while when I was in college. The main thing is, I know just enough to mess with it but not be dangerous.
I'm not sure my explanation of why the breaker is tripping is 100% correct. It's been way too long since I studied inductive circuits (like 27 years). Perhaps a more experienced electrical engineer can bail me out here. The one thing I am sure about is the difference between the regular switch and the motor starting switch with regards to that air compressor. Your converter should behave the same as a motor.