Runcam 2 lens cap printed in ABS and gives a satisfying "click" when it is snapped in place. If anything the tolerances may be a bit tight so it can be quite tough to get off again!
It only weighs 2 grams so print at 100% infill. More than likely it doesn't matter because no wall is more than a few millimeters thick and it will be 100% infilled already.
Try printing in the finest Z resolution because the snap on ridge benefits from being as smooth as possible so it can be removed easily.