That turned out good Mike!

Since a single surface does not really expect to be closed in that way either in 2 pieces like you did is a good way, or another way is to build it to be almost closed but leave just a little bit of space at the end and then put in blend surfaces to finish it up.

Check out this previous thread for some examples and previous discussion:
http://moi3d.com/forum/index.php?webtag=MOI&msg=4326.1

- Michael