Our coach parked in Kingman, Az, right now. Put down sections of 2x12 under jacks.
Well. it looks dry and is dry on the surface. 2 ft down is hard pan and water flowing over it. The 2x12's cracked and the whole shebang sunk a foot. Moved and put long 6' sections of 6x6 across the back under both jacks and across and under the rear jacks and long 6x6s sank.
A while back one of many postings on jack pads noted that those leveling blocks will bend and crack and break and sink on even much harder surfaces.
There is two or three mfgs who make pads for those big cranes etc that also make smaller ones, thick heavy rubber and tough urethane and other material pads.
Not cheap and not light. I've about decided on about two layers of glued and screwed treated 1" plywood about two feet or more across and as long that will between the tires...might not sink or break even on soupy ground. Don't know how I would lift it or manuever it....maybe lots of workouts after they fix my back, or maybe adopt a 14 year old body builder..