I am putting an addition on my daughters mobile home.I want to run mc cable underneath to the addition.What type of box should I use ? Also how far apart on the walls should the outlets be and at what height. Thanks turk

12" to the bottom of the box. However, since we don't know your wall layout it's hard to tell you where to place outlets. On straight runs, outlets can be up to 12' apart. There are a number of requirements regarding corners, short walls, doorways etc. Suggest you get a basic wiring book at Home Depot, Lowe's or your local library. It will discuss required layout.