Scooters under 50cc typically do not need driver endorsements. The shorter wheelbase and smaller wheels make them less stable than motorcycles but are great transportation in the city or slower roads. I carry an 1000cc sport tour, 150cc scooter and occasionally a 70cc scooter as a toad.
I would suggest getting an enclosed trailer so the things you bring are out of view from theft and out of the weather. Your water toys will determine the length you need and can be suspended on your walls or ceiling. My suggestion is to match the width to the camper so you can see it behind you without needing cameras or extended flags. A tandem axle trailer will track better but is overkill for the weight you are carrying. Regardless of the number of axles, get trailer brakes on all the axles to help slowing.