Made some new hubcaps after losing one of the old Volvo ones.
Looks pretty good, I'd say.
Six Neodymium magnets spaced evenly around the wheel. Each is atop a small piece of 3m tape to keep it from sliding. Three strips of thin insulation fill the gap between the rim and the wheel cover, to keep it from sliding/moving. You can see the insulation peeking out just a bit.
The eventual plan is to paint them white. They are very secure. Requires a screwdriver and a bit of effort to get the magnets to let go.
Total cost was ~$35