Redesigning Custom Post Type “Add New” page

I’ve been browsing all over google for a solution to this. I’m writing a custom post types plugin for work to log-in visitors that we get. I initially wrote a mock-up without custom post types, then I came around here from a google search and saw a screenshot that showed an example of custom post types to store information about Attorneys. It showed that someone redesigned the “add new”/”edit” page for custom post types with a whole new interface.

Using add_theme_support inside a plugin

I’ve created a custom post type as a plugin and released it into the repository. One of the core features involves using a featured image. I’ve added thumbnail to $supports in register_post_type(), so the meta box shows up in the Administration Panel. I’m also hooking into after_setup_theme and calling add_theme_support( 'post-thumbnails' ), but I don’t think it’s taking affect.