I put it together today out of a scrap piece of 2x8 I had. I had to include a short piece of 2x4 to do what wanted to, but it worked well. I didn't make the front square because I feared one of us might accidentally pull it off the front, and I feared a square front would make it kick up at the rear and damage something. The only negative is that it weighs 25 pounds.
The trailer was parked on a sloped section of our property, and my wife used this to level it with no problems. I hope we never need more than 4.5 inches.
But how about chocking? If there's not much of a slope, is it safe to chock one side only?