I started by drawing a line parallel to the outer perimeter to help me line the panel up with the bulkhead. I chose the way of Tom Martin and Randy Pflanzer and put the panel behind the bulkhead where it will sit flat, but this means the possibility of chafing for any baggage pushed against the bulkhead flanges - might have to put some tube around that.
Installed # 8 nutplates on the rear of the panel.
I also intend to mount one or two 12-15" deep but lightweight tubes on the back of the closeout panel so I can fit slightly longer things in the fuse (such as fishing rods). They'll need to be above the floor level so that small things can't roll in and get trapped back there where I can't reach them.