Quetion re: pad for tires on concrete

I began preparing a pad out of pressure treated lumber for our MH tires to sit on rather than sitting directly on the concrete pad. My thought was to use PT lumber to make it weather (last) longer. But, am now wondering if it is wise to make the pads out of pressure treated lumber. Is there a chance chemicals in the PT wood might leach into and damage the tires? Any one with thoughts about this?

If this is not wise, what would you make the pats out of that would stand up to rainy weather? Thanks! / Larry