After I designed this, I found the heavy duty, probably hydraulically operated, version on You Tube. Their version uses lock pins. My version counts on the gearmotor to prevent creep back. I will have a red light in the car to tell me that the trailer is pulled up tight, and if it creeps back, the light will go off, and I will push the "Draw Up" button. But I think the gear reduction in the gearmotor will be hard to run backwards through the all thread.
Here is the commercial version: