OK I think I've given up. I went back to cloning the original DJS stove, but I cannot get it take colours from the in-game one. It still says the object is undesignable.
The funny thing is, this object only contains a shadow texture now, and still shows up with the default texture.
I'm sorry edejan, for taking so long. We need more competent people to lok at you request, it seems. :(