Just thinking out loud on how to put things together.
I want no outer stitching showing on the velvet, so all of the boning will go on the inner twill layer. The velvet layer is then basted to the twill layer and the pieces treated as one.
The question is to flat fell or not to flat fell. This isn’t a tightlacing corset so it doesn’t really need it, but the only way I can think to keep it from showing outside on the velvet is to do it seam by seam and then baste down the velvet layer afterward.
I’ve looked at harmanhay ‘s purple velvet underbust and all the posts on that which has been very helpful. After staring at the photos for a bit it looks like regular seams with the allowances tacked down to keep them in place but I might be wrong about it.