I prefere aluminum over the steel. Steel will rust eventually unless its Stainles.

Take some 2mm thick 90* angle and epoxy it with a layer of glass cloth or you can even glass it in the bottom on both sides to make a rail. That way you can work the metal to the desired position but it still remain strong. Predrill everything and use some insulated mounts. Some folks don't even use them, but it'll cause bad vibrations for the radio equip. You could even try some thick radiator hose cut in sections to build your own insulated mount.

Just trying to give you some ideas is all.