If there is a drain tube, the pipe comes out somewhere along the outside edge of the trailer beneath the wall. If you see the drain tube going from the AC toward the road side it should be pretty close to going straight out at the shortest distance. If there is a window it will jog to one side. If it hits in the wheel well it might be there.
I have had insects fill the tube at bottom end. Try using a short plastic probe to clean out the end. Or, try a vacuum to suck the trash out. If that does not work, try compressed air to blow it out. Be careful if you try to use a wire, it can puncture the tube and cause a leak.