While stuck in the house yesterday I decided to have a play with Fusion 360.
I made this design for the Inspires Polar Pro ND filters.
These are screen captures from Fusion.
Insert, I could have made this as one with the base but I wanted a different colour and to put some faux suede cloth between them as to not scratch the filters.
And the finished item, printed in a wood mix PLA with a white insert.