[scook]

No idea if this is useful in your situation, but additional support might be made using PVC pipe. It can be bent to hold a curve, using heat (electricians use a special heat blanket, but CAREFUL use of a heat gun works). You can cut the back out of “T” fittings to rest against real rails, etc. and adapt to larger or smaller things to rest on using adapters and larger or smaller T’s. A “T”, cut open can also be heat bent to rest on something that’s not round - think of it as working with Keydets to make a sheath or holster.

Hope this is helpful, if only to get you thinking along different lines. If this seems useful, but not very well explained, shoot me a PM with your email address and I’ll answer questions as well as I can - can scan and send some sketches too, or have a phone conversation.