For a comprehensive review on mounting and dividing very large staghorns, go to this link.
http://garden.org/ideas/view/d...
For my next outdoor hanging specimen, I am considering some type of heavy-duty, non-rusting, hanging box-cage type of frame. Will fasten some of my divisions inside the frame structure and just let it grow outward. I won't have to worry about rust, hanging chains, etc., and future plant division will be easier. In my experience, it is best to have a 3-4 chain support for balance and leveling since they will tend to grow lopsided over time.
Will post an image of one to the above mounting link when I build it later this spring. I think an 8-12 inch wide box frame of aluminum or stainless should suffice because I want the fern to encapsulate the frame in a few years, with eye hooks on the corners to easily adjust and secure the chains.