One potential problem with a trailer parking brake is the same as that
with parking brakes of motor vehicles that are left sitting for long
periods. The shoes may stick to the drums from rust. I have had a car
that sat for years with the parking brake on, and when it was to be moved
the brake refused to release. The mechanism or cable wasn't jammed; it
was the shoes stuck to the drums. Clutch disc linings sometimes do the
same.
I suggest that if your trailer is going to be sitting for a long time
without moving that the wheels be chocked and the parking brake
released.
Electric brakes are largely self-energizing, that is, the torque of
braking applies the shoes against the drum with much more force than the
lever presses the shoes against the drum.
Most drum brakes, electric or hydraulic, are partially self-energizing.
Al