I believe Dutch recommends #40 drill cloth as part of his system. It's usually available at Joann's fabric store, usually near the pillow ticking. A few years back I purchased Dutch's materials and got into his system and found it to be very good. The drill cloth is 100 percent cotton and very tough, and most I have found mikes at around 0.018 thickness.
On a somewhat related note, I was in Joann's a couple days ago and they wanted $15 a yard for ticking, which seemed crazy to me. Just a couple of weeks before it was $6 a yard.