Kiteboard building also? I build those too, and the twin tips are done with a vacuum and when done right you can get a near perfect finish, but unfortunately I don't think I can make this work on a SUP.
Here's a video I made a few years ago, this is the one about glassing. See around 4:30 how I get a one-shot near perfect finish. Like I said, I don't think this will work on a SUP
I can build a twin-tip kiteboard in 4 or 5 hours of labour!)
Peter