Having back problems now, I realized I needed to stop manhandling full sheets of drywall and plywood. I came up with an easy solution with a panel carrier and one caster.
The caster is 4 inches in diameter and 2 inches wide. The 2 inch width works out very well for rolling through the grass without bogging down.
The 4 inch tall caster rolls easily over large cracks and thresholds.
I could have easily have made a panel carrier to lift with, but I already had one. Now I can effortly transport plywood from my truck down to my walk in basement, and back out to the back yard to set up on sawhorses for cutting.