Framing

I chose to add the framing on the inside like a standard home. It does cut down on finish space inside but felt it was the best option. I also used a wire wheel on a grinder to get rid of any rust spots on the wall and used some oil based primer to seal it. Then moved on with the framing.

This shows unfinished/storage side of dividing wall

This pic shows the finished side of dividing wall.

For the ceiling I wanted plenty of insulation and needed extra space for it. So I used 2x6 for the joists. All of the framing is approximately 1/2" out from the container steel. All the openings were cut with a 4" angle grinder. The openings are 4" larger than the rough opening size to account for the 2x2 14ga steel frames that I welded and installed first. The door opening height needed to be cut just right to end up with a finish floor height at the inside plywood height for the door to be installed. 

The framing around the door needed to be set just right to align with the 5 1/2" jamb thickness. The studs are 3 1/2" and the 2" to the outside of the steel frame. 

After the steel frame was welded in I used OSI Quad caulk on the inside and outside. It's an excellent exterior grade caulk and stays slightly flexible. I also welded a little bit of angle iron under the door sill as a sill support. 

I also welded a drip cap over the door to keep the leaks minimum.

I still have to grind the rust on the outside, remove the stickers and paint the whole thing. But it's getting there.