I think you have the infamous "unobtainium" lock, but there may be a fix.
First (obviously), you'll need to be able to get into the trailer, the door should still open from inside. Does your trailer have any access compartments on the outside? If so, you can open the compartment, and a small child can get in, go to the door, and open it for you.
If you have no hatches to get in, are any of the windows unlatched? Again, a small person can crawl through and get the door open from inside.
Meddle not in the affairs of dragons, for you are crunchy, and taste good with ketchup.