i have to install a flush mount 50amp oven receptacle. I'm not sure what type of old work box I should use. A 2 gang plastic old work device box? A metal 1900 box? What type of old work box would be able to allow a 6/3 romex cable to be securely fastened to it. This is an "old work" job....fishing wires between walls. The homeowner wants it flush mounted. Some suggestions would be greatly appreciated!!!! Thanks!!