Question about lowering unhitched 2 wheel travel trailer

I second what Mitch said. I would never use a cinder block to support anything like a car or trailer. I had a shop teacher back n the 70's that would jack up his own car and place a cinder block under the frame. After lowering the jack, he would tap the block with a light hammer. The cinder block would shatter and the car dropped to the ground. I never forgot that.