Clamp your SDRplay RSPduo with two broom mount clips to any mast of between 20 and 30 mm diameter and secure it with two cable ties. 

The two broom mount clips are of an ubiquitous type (distance between the two mounting holes 37.5 mm, total length across mounting holes 50 mm) available e.g. at Aliexpress and Ebay. Apart from the two broom mount clips you will need four M3 x 10 mm screws and four M3 nuts.

No 3D printing supports required.

As always I include the OpenSCAD source file for you to adapt and/or improve:

• Download and install OpenSCAD from https://www.openscad.org
• Launch OpenSCAD and open the enclosed OpenSCAD source file (/File/Open).
• Amend the parameters at the top of the file or even amend the code.
• Save your changes (/File/Save).
• Render the design (/Design/Render).
• Export the rendered design e.g. as a .stl file (/File/Export/Export as STL).
• Slice and print.

See my other designs at
https://www.thingiverse.com/thinger13/designs

In particular:
https://www.thingiverse.com/thing:5472960
https://www.thingiverse.com/thing:6354215
https://www.thingiverse.com/thing:5787042
https://www.thingiverse.com/thing:4924478