It's quite common to have a lockable top box on a motorbike. Many e-bikes have a rear rack for the battery but I don't see any with top boxes but I see that they are available. Years ago when I was mad enough to ride a Norton Commando I had a top box on it that took two full face helmets which wash any when you stopped & didn't want to carry your helmet about. Something that would take a cycle helmet would be nice. Does anyone have any recommendations?