I can speak for the Southern USA in regard to steel coil transportation as I live in the Birmingham, Alabama area of the USA. In my area, the steel coil cars are Gondolas, either open or covered (which is normally called a coil car). In coil cars the coils sit down in a trough with a sliding bulkhead to keep the coils from moving around in the car, and the lid would sit down either over or between pins to keep the lid in place with the aid of gravity.
An open gondola is just your basic gondola car that has had racks welded into the bottom for the coils to sit in. There are cross sections welded in to keep the coils from moving to much, and not all of these cars have bulkheads to tie the coils down. In that case the coils in each end would be tied together to lessen movement.
Here in the USA, we would ship tubed steel, flat steel or sheets only on a flat car, usually a bulkhead flat car, which is why when some people load steel on a flat car it turns into sheets instead of showing up as coils.
also a note that I have never seen aluminum coils carried uncovered. Every load I have seen has had to be protected from the weather.
I don't know everything about the subject, only what I have actually been involved in, so to the best of my knowledge this is accurate.
Don Malone