My idea would be to help the car see obstacles, rather than protect it from touching unseen obstacles. Hanging foam or carpet on the walls will definitely make the car work harder to identify obstacles.
I still don't understand how on some videos I have seem summon actually crashed to well established fixed walls that ostensibly reflect acoustic signals. It's as if some percentage of the time it just does not see very real solid objects.
Crazy that these sensors will be counted on to avoid accidents when they crash into walls and pillars during low speed summon maneuvers.