You state that the garage breaker is the one tripping. What all else do you have running on the circuit in the garage that supplies power to the outlet?
Have you bought a freezer or anything else that is now using that circuit...... especially a window unit air-conditioner in the garage.
You could be close to overloading that circuit BEFORE you ever plug the trailer into an outlet there.....and thus the trailer is enough to trip the breaker.
Also, as Lou correctly pointed out, are you using any kind of extension cord from the trailer to the outlet? Your problem could easily lie there in the extension cord.
2011 Flagstaff 831 RLBSS
I used to be addicted to time travel, but that's all in the past now.