You'll totaling love the process of building a WFO, and I wish I would have collected wood to season the same time I searched for materials. I found the majority of my items in Dallas about 90 miles away. Check yellow pages for insulation materials, also search the web. James (FB) has found two new products since I purchased my material, FR Board and Blanket; they cost probably half what he had previous and are competively priced. I don't know about shipping though.
Welcome and enjoy the build. Oh by the way is the dh your designated hitter?
