This photo shows the scooter on the platform with front tie-downs in place.

Notice that one tie-down is attached to the handgrip towards the front of the camper and crosses the scooter's front to the rear of the platform. A second tie-down crosses the scooter from the left handgrip to the front of the platform.
A third tie-down is sufficient to secure the rear of the scooter by passing from the front of the platform to the rear looped around the the small chromed metal carrier behind the scooter's seat.
I actually secure my tie-downs to my spare tire, but didn't show that configuration since many people won't have a spare tire in the right place for that purpose.
It is practical to travel with the scooter secured as described above; I did so for many miles.
However, because of some personal physical limitations I added some improvements. An important improvement was the addition of the horizontal beam on the scooter's floor in the photo above. This beam clamps the scooter to the platform. An electric screwdriver & deep welled socket are used to tighten the clamp.
The electric screwdriver is seen just below the platform in the photo above. The clamp assembly is built from standard hardware.