We've sunk with 12x24 pieces of two pieces of 1inch plywood screwed and glued.
Last time was just west of Austin in the hills. Ground looked dry and was but a ft or so down water was flowing from recent rains on rock. We sunk the jacks a good two feet or their limits.
We sunk the mh on big 12 in wide boards in Michigan over two weeks at Relatives home.
These little pads won't fill the bill.
The pads we carry are wood 12x18. Little loops on ends so they can be pushed into position or pulled out with awning rod.
Even on asphalt we have seen the jacks sink an inch, especially in the Southwest.
The only reason we don't carry larger pieces of wood is there is not enough room between jacks and tires in back or space in storage.
And ...our coach is nowhere as heavy as a the 45 fters.
That is perhaps the reason many sit on the axles now and jacks just steady the coach if they even have them.