some seeing eye wrote:Weld some bolts on the angle iron that forms the top corner, bolt rail to that, cantilevering the rail post down the side of the container. You can grind them off when you sell the container. If you set the depth on your drill, you can drill the top edge angle iron in the spots where there is a negative space in the corrugations.
You never know what kind of clamps you can find at a scaffolding, machine shop fixturing, or welding store. You could build a plywood and lumber floor for the roof and work your bolting off that. Be sure it does not blow off.
The size of the top edge angle iron varies between containers.
Better yet, weld nut to the inside of the angle iron, where the corrugated steal sides go inwards, that way you have no protruding metal, and nothing to get damaged. Then you're railings will be a bolt on affair. Also as noted you will need to make a platform for people to stand on, as the metal ceiling of the container is not strong enough. Plywood, and 2x4 will suffice for this, and could be built on playa if you're careful with sawdust.