This is the best 'zoom-able' pic I can find.
The rails are supported by the pipe work which is held in place with brass Munson rings. Copper to irons on each end, and as a belt n braces job I created a ring so the manifolds got fed from both ends. I did that as the cold manifold was very long and could have suffered loss of flow and I just then carried that across to the hot manifold to as it was easy enough to do.
The remit on that job was to be able to use all the showers at the same time and still have some useable flow / pressure elsewhere so went to town on this one.
If you zoom in you'll see opaque / white plastic spacers in between the manifolds ( 3 to the long run ). These iirc were 28mm Talon pipe clips which held the rails with near spot on results. Another way to do this, if only feeding from just one end, would be a clip on the input pipe work and then a stub of pipe made off and cap ended ( or a DOC ) the other side, with enough pipe to get a second clip on.