Looks great! As for finishing the interior, a friend of mine has made a habit of using epoxy-bound materials on ceramic, pvc
, clay, etc to make some interesting tubes, caves, and other decor. He coats the areas he wants to treat with an epoxy and then uses anything from sand to small crushed stone or small gravel and applies it to the epoxy coated areas. All of the pieces he's made are really quite impressive. I know for sand or similarly fine mediums he puts on two or more layers just to cover them thoroughly. He's made me some stuff, I'll see if I can dig up some pics and post them here.