Since I've had to put 4" of pink foam in the pickup bed to accommodate the higher cab on my Ford, I'm nearing the maximum travel on my jacks. An inch or two would really help. What to you use, if any...
I use 24" x 24" plywood with a small piece, 6" x 12", on top of that. My wheels run over the bigger plywood with no effect and the front jacks sit on the smaller plywood. I've got maybe 1" of clearance between the fender and jack. Rear jacks on 2" thick concrete block. For more clearance maybe a 6X6 under the front jacks, or two.