Cut a 15 mm heating pipe to size and print two supports (support material needed for the inserts). With two M4 bolts and nuts, you're all set!

The 15 mm heating pipe may be a typically Dutch product, I don't know.  https://www.gamma.nl/assortiment/thermische-cv-buis-15mm-3-meter/p/B995551 

The pipe used has a wall thickness of 1,2 mm. So the outer diameter of the support is 12,6 mm. The FreeCAD file is included so you can change dimensions in the VarSet to your needs.