You may get some insights at the following:
Did you install the AC youself?
Does it sit in a plastic condensate catching pan, or does it have a couple of little cups mounted under it to catch the condensate?
When you say it is draining on the outside, do you mean you can see condensate running down the outside of the trailer, or is it coming out of the drain tube (which should be located near your wheel well on the street side)?
Are you seeing a steady drip, steady stream, or just a few drops occasionally?
I have a problem with my AC creating condensate that drips down into the trailer on really humid days where I am coming in and out of the door a lot. It isn't a matter of the drain not working properly, it is just that the air is condensing on surfaces that aren't designed to catch liquid, so it just drips.