I use GWD all of the time and while the interface is slow, I'm able to create some very complex banner ads under 40-60k. I'm learning green sock because of the Sizmek ad network and I recommend NOT using their GWD/Sizmek workaround pdf. It's actually outdated.
I wonder if I were to open a new file in GWD just as an HTML doc and code with Greensock. Haven't tried it yet but I hope that I can still use the preview tools.