it'd be great if 3d formats were supported by the site itself. But if that's too complex, either sketchfab or marmoset(haven't tried it yet) seem like a good option. And even though sketchfab's TOS don't allow most adult content, there's an option that allows models to be hidden from public but still viewable/embedable if you have the link. You could even protect them by password. Maybe that isn't a full solution, but it could be a workaround to make this possible