I'm currently working on adding Steam Workshop support for custom environments, and I figured I'd give you all a heads up in case you want to start chipping away on a personal studio or even outdoor environment you'd want to paint in. You will just have to deliver the environment as a single .glb file, in which all the models and textures are defined. You will also be able to supply your own skybox and ambience. Just modelling & texturing in Blender, and exporting as a .glb, will work perfectly. Be sure to bake the lighting as well, as there is no real time lighting in Vermillion.
You can get the template file here which shows where the easel goes and which direction it's facing.