Lost key

A couple friends of mine lived in a trailer I had for a couple years. They moved out out of state and I now have the the trailer in storage. When they moved they lost the key to get into the main door. What would be the best way to go about getting a new key? Should I meet a locksmith at the Trailer and have him make a key there, or are a lot of RV locks pretty universal I could get a key online? Thank you for any advice!