Ideally, having ASA certification thru ASA level 104 (Bare BoatChartering) would give you a ticket to charter a boat within 5-10 ft of the size boat that you trained on. For example, if you trained on a 30 ' boat, you will probably be approved to charter up to 40' depending on your resume. Many schools combine ASA 103 (coastal cruising) and 104 into a one week live aboard class. If you feel a bit rusty & want to get a refresher in environments similar to where you will charter, that would be a good way to go. As Capta & Roland mentioned, you will likely be approved without formal certification, especially considering the length of time that you have sailed & that you own a Catalina 30. That being said, the charter company may restrict the sailing territory (no Anagada in the BVIs)
And if you want to charter in Europe, forget it, you'll need more than an ASA ticket. If you are just looking for a sailing vacation for yourself the ASA 103/104 combined live aboard course is fun. There are a bunch of schools in Florida that do these, even in winter. Finally, as John mentioned, best to call the charter company to get the facts as to what experience they require. If you feel a bit unsure, they can also put a captain aboard for a day to get you up & running.