Should be printed on the side in a flexible material like polypropylene or TPU.
I used FormFutura Centaur Polypropylene and it has the right flexibility for it to work perfectly. There were some adhesion issues, though, so I would recommend a brim. There is a version of the model with an included minimal brim for easier removal.
The printed feet can be attached with double-sided tape.
The author marked this model as their own original creation.