I think side rails would be great. It could be made flexible enough to be 4’x 8′ but could be anything smaller. I am thinking “A” frames on the sides to support the X and Z but allow for the X to be moved for narrow pieces. It would not be hard to clamp the conduit on the ends of the boards to lock them in place. I am hoping this triggered a new project since you have done a AWESOME job on your other designs.