Is it going to be curved at all, or just straight? I have yet to touch Worbla so I can't speak to that, but there's a lot I won't do with Wonderflex (and honestly I'm really not enjoying the newer configuration of it). If it needs to stay flat or straight, I use sintra or styrene instead.
If you're shaping it at all, Wonderflex does hold its shape fine after heating, but it usually comes out fairly uneven thanks to being so thin and easily-heated. I always end up with fingerprint-pits marring my would-be smooth shapes, which is why I only use Wonderflex if it's going to be covered in something, like fabric, that will hide its flaws.
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