Just a thought on an improvement to rigidity, what about the possibility of reinforcing the existing conduit with something like angle iron? It is simple, cheap, and there would be no need to dramatically alter existing machines’ designs. It could be used to line the inside with tripod like support.
The use of conduit is a big part of what makes this as affordable as it is. To go with extrusions or carbon fiber would greatly increase the price at first build and to modify it later.