I've seen plywood break under jacks. I'm looking for a nice, low cost piece of 2'x1', quarter inch plate.

I also keep a rolled up blue ground pad in the truck for kneeling and sitting and tool space, not to mention it is a 6'x2.5' blue rectangle- it will be seen at a distance, that is not a shape/color that occurs in nature. Unless your monolith is really, really cold.