You trailer ceiling may be insulated (a little bit), but your AC isn't. Open the access cover to your AC, look up, and you will see no insulation. Only thin sheet metal between you and the inside of the shroud (which has lots of holes in it).
Every fall, I insulate the inside of the AC with a foam/reflectix sandwich (foam in the center and reflectix on both sides of the foam). Completely eliminates the cold air dropping down out of the AC. Cold surfaces + moisture (respiration) equals condensation. In the spring, I simply remove the insulation. I seldom use the AC, so if I forget it's no big deal (I unplug the AC to insert the insulation so it won't run anyway).
Hope this helps.
