So you have 2 wood crosses held together with clamps
and you use those adjustable ropes to hold up the two lens tubes
and you are saying that you just need to accurately hold up the camera to the tubes ?
I hope the wood doesn't slip or anything, any jar would make those slip.
and of course the adjustable ropes are not holding the tubes up very accurately.
I think this would require quite a bit of extra setup than needed.
Why not just use the adjustable ropes to hold the tubes against the vertical 2x4s.
That would eliminate any issue of the clamped cross pieces of wood from slipping,
and with the lens against the vertical, the adjustable ropes would only need to compress the lens tube against the wood instead of holding it up in mid air.
or get a cheap monopod