Well, if the mission is a transport one, avoidance is probably the best strategy. Huey's are, as you've seen, very vulnerable to AAA. They're not really designed to handle that. If you have to destroy them, I would probably loose salvos of rockets from afar and try to get lucky. I don't know if the guns do any decent damage to 23mm emplacements.
Another dangerous strategy if the terrain is friendly, is to use the terrain to mask you until you get very close, then pop up and fire a lot of rockets quickly and dive back behind cover.