I too have a 23' TT with a 15K BTU air. It was around 95 today with like 90% humidity. I've been working in the trailer in the driveway all day going in and out. The temp inside has stayed below 68 all day.
If you have ducted air make sure none of the outlets are closed. If you have moisture at the return air vent (I assume you mean in the ceiling unit) I would suspect you may have a freeze up issue. You can remove the filter grill and look at the evaporator coils to see if there is ice forming on the coils. That would allow moisture to drop back as the ice melts.
Freezing is most likely caused by insufficient airflow over the coils and is exacerbated by the high humidity.
Make sure the filter is not obstructed.
Make sure the fan is running on high.
Some units are poorly sealed between the return air and supply air side of the air distribution system in the plenum. This too can cause freeze up.