how is that trailer attached to the Vespa, and will it just beat the hell out of the Vespa during braking and accelerating?

Found on http://goawaygarage.blogspot.com/

Maxx knew the answer, Stabil, by Marchetti.

The braking system is implemented through an inertia system: during deceleration, the trailer wheel advances, applying the controls that actuate the drum brakes on the wheels.

http://www.lancia-ardea.it/OldSite/Rimorchi.html

http://www.vesparesources.com/50-sidecar/26364-e-uno-stabil-marchetti-originale