When you move the wheels back you will be making a longer bridge between the car and trailer wheels. At the same time you will have less overhang behind the wheels. I would think that would lessen the movement.

The bridge between the car and wheels will need to be watched simply because it will be a longer span, flex more, and more inclined to break if over flexed.

Were it mine, I would move the wheels then load and find the roughest road around to give it a smoke test close to the welder. CB