I think the OP simply wants to keep his tires off the dirt when the RV is not in use.
I have gravel under my tires. No, not a gravel pad the full size of the coach, just four spots of gravel where the tires sit. It works for me.
For what the OP wants, I would cut 10 pieces of the chosen boards about 3 feet long (after thinking about it, 2 feet would probably be plenty!). Put them side by side, 2 each for the front tires, 3 each for the rear tires, then tie them together with heavy duty (1/8 inch thick by 1 1/2 inch wide) galvanized steel straps secured with 1 inch wood screws. Use at least three straps per joint, more if desired. Installing the straps on both sides of the boards (2 on one side, three on the other) might not be a bad idea, but IMO it probably isn't necessary.
Coat the boards with a good preservative paint or stain, place them where they need to be, and drive up on them.