Recent reading on similar topic lead me to try an Ace wrap (could have been here).
It was for a fiberglass epoxy lay up of a rounded fuse top. I had a wood version to use as a shape mold.
stuck the orignal in a bag, pulled a nylon knee high over that, (left over from my bank robber career) light spray of 3m77, a single layer of some med weight fiberglass and a second knee high. Wetted it out with epoxy stuck that whole works into a bag and then Ace wrapped it.
It came out fine. it retained the dark color of the knee high
(Darker stockings disguise better[8D])

Long way to go, but it would work just fine for shaping balsa too!