For closed cell pad, look for a blue foam "sleeping bag mattress" in your local big box store or sporting goods store. It'll be in the camping aisle. They are on the thick side, ~3/8" thick, approx 30" wide x 48" long.
...or look at that non-slip rug pad I mentioned.
And Denny, looking at pictures of your beautiful truck, I seriously doubt you'll EVER have a "greasy starter" to contend with.
Bill
