Is your A/C Ducted throughout the Trailer, or is it simply in the middle of the ceiling where it blows cold from there only?
I agree 100-pct with all of the above suggestions, but want to add that the Ducted ones have Frost Sensor that's meant to stop the cooling so it won't freeze over.
If there is a sensor, it could be operating normally, but it's very common for them to fall out of their designed location near the cooling coils.
If it's at all humid out, run the A/C Fan on HIGH, just like they said above.