I have made every single unusable space in our 25 foot travel trailer into either a usable cabinet or usable drawers, and I even added a floor to ceiling unit as you come into the trailer where there was wasted space.
It has four drawers on the bottom and cabinets with shelves on the top with an electrical charging station in between
In almost all the factory cabinets I have added extra shelves.
In all our wardrobes, I have converted them to shelf units.
Now we just bought a new 2016 37 footer, and I'll have to start all over again
Jack L