We had problems with the 13.5K unit that came on our 27' 2001 Safari. First trip ever with the Safari in 100 degree full sun, we couldn't get temps below 85-89 until the sun went down. Parked next to me was the folks who bought my 30' SOB equipped with a 13.5 K unit. They were cool as cucumbers.
Took the trailer back to the dealer and finally Jackson Center. No problems found. I also found however no standard engineering factors from Airstream in regards to expectations from the A/C unit. Bottom line I added a large Zip-Dee awning on the street side of the trailer from end to end. I never had problems after that. Too much exposed aluminum.
When I purchased my Classic, I upgraded to the 15K AC unit. Up to this point we have never had any issue regarding cooling performance. I do however, continue to extend all the awnings out on all sides when out in full sun conditions.
Airstream did note that they have had situations where the refrigerator compartment was not sealed properly which allowed heat from the compartment to migrate into the trailer. That's why they asked me to go up to Jackson Center so that they could make that inspection.
'04 Classic 30' S.O.,'03 GMC Savana 2500,'14 Honda CTX 700