Another option is to have a receiver hitch installed on the front of your rig. You can then get one of those "cargo trays" that fit into the receiver. They are roughly 4 ft wide, and plenty strong enough to hold a scooter or small cycle. Easy to load and unload there, and it doesn't get in the way of your boat or trailer since it's in front. A little more costly than a rack, but also more versatile.