Yeah, making them yourself is the only way to go. The way to get the most out of a given amount of space is to have all your stuff fit exactly. And if you build it yourself you can keep revising it after getting experience using it.
May we ask what your purpose is? Do you need the barrier for pets or other animals? What kinds of special problems do you need to solve? And what do you want drawers for? Drawers tend to waste space since they usually aren't filled to capacity, but they can make sense if frequent access is necessary - otherwise, a soft-sided stackable container is more efficient.
I'm working on converting my newly-bought KJ into a camping/fishing vehicle. Since part of my end result is a wide open interior to sleep and camp in, I don't want to have too many fixed structures. So instead I'm building stackable structures for the various components that fit together nicely.
Oh, one tip, if you're in need of space - remove the paneling, especially in the back. There's lots of extra room behind it that you can use.
