1 inch treated plywood sections, with a smaller section glued and screwed on top of that as large as will fit a small compartment, that will go under your jacks and not have to run the wheels over them.
They get heavy but plastic ones like utility companies use on outriggers cost a ton.
In Texas we stayed at an RV resort outside Austin that was perfectly dry and had large rocks on the lane on the site. Our front jacks sunk down to their limit. Water running over rock a few feet down a week after a downpour.
They brought big pieces of plywood plus ours and some boards after re situated on the site a few feet. The grass and lane were bone dry on top.