The cleaning seems to have really helped. I am now getting a temp reading of about 57 degrees coming out of the air vent and maintaining a 74-75 degree temp in the Airstream. this is in 95 degree outside temp high humidity here in Houston TX. I also think cleaning the dirt that had built up in the cupped blower blades has increased the air flow as well. As an added measure I also insulated the top of the plastic inner cover where the chilled air enters the blower and is discharged in to the trailer. I noticed while the outside cover was still off that condensation was forming on the the outside top and sides of the inner plastic cover so my thought was to try and keep the cold air as cold as possible. I used reflect-it silver bubble insulation cut to fit and silver tape. I then insulated what I would call the air box area on the inside of the trailer where the cold air is discharged out of the front and back vents of the ceiling cover with reflect-it as well. I am not sure that either of these will provide any additional cooling effect but I felt it could not hurt. So for now the Airstream is cool and the old Carrier 15,000 BTU AC is pumping out cold air.
I am now a firm believer that maintenance on the critical systems such as your AC must be done on a regular basis. Otherwise they slowly start to degrade and will wear out sooner. I plan on making this an annual event from this point forward.
1976 31' Sovereign