It took me months to source this vinyl when working with Ord Mantell. I had only bought 3 yds at the time. I have played with the thought of somehow using clear vinyl, since that is actually smooth. But this was the smoothest *white* I could find. The company I got it from hasn't had anymore in stock since. I regularly check in with them to see if they've got any more. No luck with that.
But your belt is looking good. The best way I can recommend to make it look "smooth" is to slather on a couple more coats of paint.
Grue Grimman