I decided that I didn't want to cut holes in any of the plates until I'd formed the firebox wrappers - so I started on those next. One way to form them is to make a wooden template and beat the annealed copper around them. Or you can form the sheet using bars of the appropriate diameter, which was the way I chose to go ( not being an enthusiastic woodworker !)
Once annealed, the copper is incredibly soft, and needs little more than hand pressure to start to form it. I used various formers, as the pictures show. This firebox has a combination of inside and outside curves (most do) which makes it arkward.
I just bent a bit at a time, checking against the flanged plates. A good fit is important, as silver solder has no gap filling properties.
When the copper stops bending easily, its time to re-anneal. It took me five or six heats to get the inner firebox wrapper to my liking - less for the outer.
Incidentally, I deliberately left the sheets oversize; putting lots of bends and folds in sheet is difficult enough without having to worry about having enough length - the first fold on my outer sheet ended up 1/4 inch from where I'd planned it, so I was glad of the excess. I won't trim the excess length for a long while yet.