Trying to create a custom post type, post type box doesn’t show up?

Try changing this:

add_theme_support( 'post-thumbnails', array( 'post' ) );

to this:

add_theme_support( 'post-thumbnails' );

IIRC, that array is explicit, meaning that by including only post, everything else is excluded. But if you omit the array, then post-thumbnail support is added for all post-types that support them.