It sounds like you’re easily in single-axle territory, and that’s nice because single axle trailers are a whole lot easier to maneuver around by hand, they don’t fight and resist turning.
All I’ve got to say about the scooters-at-older-age thing is go for it if you feel you can handle spilling the thing at some point. The older I get, the less I risk breaking myself!
The other option is getting electric bike motors. They work really well and are great for campgrounds because they make virtually no noise.