I'm learning that the secret to a very open crumb is lots of water in the dough, and bake it in hot oven with lots of steam, on an oven stone, if you can. Beyond that, it's a dozen or fifty batches, learning to handle the wet dough, and knowing when to scrape the mess into the oven to bake.
JohnF, be very sure that this is a crackly crust with a huge, moist crumb, my best yet.
A coupla more,....