Welcome to the forum, and thank you for sharing this design and ideas.
In general, I share the views that tubes are available and why complicate life with 3D printing it. Also share the view that some of these are a bit overpriced. My solution was to keep the tube in T2 (using M42 to T2 adapters), and buy the T2 extensions that are a bit more affordable.
I do not have a 3D printer, and what I have designed was printed commercially with machines that have greater capabilities than your typical home printer. With this disclosure, and my very limited 3D printing experience, I would like to offer a couple of suggestions.
- A thicker wall may be needed to avoid deformation in the long tube, and to support the arm of the lens x tube length. If this is already considered in your design simply disregard, again, my hands on printing experience is limited.
- A typical problem of the HQ sensor and long tube requirement, is a good stable support for the assembly, including rotating the sensor 90 degrees for best use of the pixel-to-frame ratio. I posted pictures of an aluminum bracket to mount the sensor and support the tube. If one were to take the trouble of printing the tube assembly, it would be good to design/include means for supporting it (a provision for a good bracket?).
Hope this helps.