I’ve installed a few Dometic Turbo self contained units in customer’s boats. Very easy install and the customers were happy very happy with them.

Since the thread is from a few years ago, I hope you've already installed an a/c unit on your Catalina 42 and are enjoying the benefits of a cool boat. However, if you're still in the process or looking for recommendations, Hot 2 Cold Air Conditioning could be worth checking out. It is known for providing high-quality boat a/c systems. While I don't have the most up-to-date information on their offerings, you can visit their website at hot2coldairconditioning.com to explore their products and see if they still have options suitable for your Catalina 42.
Remember, it's always a good idea to consider the specific needs of your boat, such as size and cooling requirements, when selecting an a/c unit.