Simple spool rack.

Fits "16mm European electrical PVC conduit" by default, but is fully customizable in Fusion360 (solid->modify->change parameters)
 

Customizable:

• tube diameter
• distance between tubes
• wall thickness (keep small enough that the wall can bend, so the tube can snap in)

If you aren't able to customize in fusion360: request a size in the comments

Optionally you can put weather stripe on the bottom as an anti-slip