Hat shelf - extension for Ikea Portis rack

I'm using the Ikea Portis as a rack for my motorcycling gear - I needed an extra shelf to store my helmets...

With the 3D printed self-clamping supports, I've mounted 3 Ikea "Hejne" stands as shelves, maybe I'll use the holes in the future to fit something else onto it (seperators, or whatever).