Back in the sixties, RV air conditioners had an inside unit & outside unit with the two connected by a 3-inch service hole. Nowadays, RV ACs are comprised soley of a top unit which sits on a 14-inch square hole.
My 50 year-old travel trailer developed a leak which I finally decided could only be resolved by removing the top portion. The tale can be followed at this link on my Airstream's web page.
