I would also recommend against Herptastic. Keepers I know and respect, some of whom have over 60 snakes, have nothing but great things to say about Black Box. All of my enclosures are by Focus Cubed Habitats and I swear by them, but they don't make a 36" enclosure that is only 12" tall.
I will say that I personally wouldn't put a Ball Python in a 12" enclosure. Being so low makes cleaning substrate a PITA for the keeper and severely limits your options if you want to give your snake any climbing or enrichment options. If you have the room for an enclosure that is at least 15" tall - or better yet 18" - you and your snake will have more choices for enclosure furnishings.