If you got 4 mowers on a trailer it looks to me like all those floor devices will get in the way for fast load and unload? YOu can't stagger them so that the mowers in the front can get past the devices to hold the back mowers.
And what happens if you need to put a backup on that is different. I know in theory all these wheel chuck devices are great but in the real world you use boards and straps hooked to the sides.
We use various versions of these;