You should look for an earlier post.
http://www.hobiecat.com/community/viewtopic.php?t=6010&highlight=wings
I have a HC18 1979, with Magnum wings (added). I purchased the boat used with the wings installed, but they seem easy enough to install. I have to remove them for racing in teh HC-18 class.
http://www.hobiecat.com/community/viewtopic.php?t=6448&highlight=wings indicates that there should be some reinforcement of the hulls at the hull/deck joint when mounting wings.
Search the forum for "WINGS". There is a lot of good advice and discussion about the pros and cons of the wings on a HC18.